AIRMANSHIP
Autunno 1999

Report on the low fuel incident of KL874, a Boeing 747-406, PH-BFC, en route from Bombay (VABB) to Amsterdam (EHAM), on 14 July 1994

Operator: KLM - Royal Dutch Airlines - Aircraft type: Boeing 747-406 Combi Registration: PH-BFC Flight: KL874, scheduled from Bombay Airport (VABB) to Amsterdam Schiphol Airport (EHAM) Date: 14 July 1994 Place: During descent into EHAM

All times in this report are Universal Time Co-ordinated (UTC), unless otherwise indicated.

Synopsis

After an uneventful take-off from Bombay Airport in heavy rain, the EICAS alerts "Flaps Primary" followed by "Flaps Drive" were triggered during climb, passing FL220, at an airspeed of approximately 330 kts. The respective emergency checklist procedure was performed and after some delay, due to poor HF communications, clearance was obtained from Bombay ATC to descend to FL200, in accordance with the emergency checklist procedure. KLM movement control and KLM maintenance support were contacted via HF radio and in concert with KLM maintenance support the flaps were recycled between positions 'up' and 5 several times, by use of all available operating modes. However the flap warning persisted and it could also not visually be verified that the leading edge flaps were fully retracted. It was decided that the flight could continue but that the respective flaps 5 limit speed should be observed. However in concert with KLM operational engineering, it was decided that the stated altitude restriction was not applicable and that the aircraft could climb, given the normal operational envelope and the additional speed limitation. An intermediate landing at Dubai was considered, but at that time the aircraft was still operating above its maximum landing weight. Fuel calculations indicated that the flight could proceed to Athens with 25.000 kg fuel remaining upon arrival. While the flight continued, it became apparent that it was also possible to continue the flight to Frankfurt. KLM movement control was informed and a technical team with spare parts was put on standby to proceed to Frankfurt as soon as the final decision was made to make an intermediate landing at Frankfurt. While the flight continued, fuel calculations indicated that KL874 might continue to Amsterdam with approximately 4000 kg fuel remaining upon arrival. Shortly before passing abeam Frankfurt, fuel calculations indicated slightly more than 30 minutes reserve fuel remaining upon arrival in Amsterdam and after consult (via KLM movement control) with the Schiphol Meteorological Office, Air Traffic Control and the chief pilot, it was decided to continue the flight to its original destination Amsterdam. After passing Frankfurt, the indicated amount of fuel remaining upon arrival however started to decrease and ATC did not clear KL874 for an unrestricted descent and approach into Schiphol. During descent it became apparent that the aircraft would land with less than 30 minutes reserve fuel. KL874 did not declare an emergency, but ATC was informed of the critical low fuel situation, after which KL874 was cleared direct to Schiphol. Due to a late descent cleararce, an intermediate level off at FL260, diverging radar vectors from ATC and early flap extension, to verify the correct operation of the flaps, the calculated remaining fuel decreased further and after parking at the gate it was noted that there was 2200 kg fuel left.

Factual information

History of flight

On 13 July 1994, KL874 departed Bombay Airport, on the west coast of India, at 20:58 (14 July 1994, 02:28 local time) for an 08:30 hrs scheduled flight to Amsterdam Schiphol Airport. The crew had arrived in Bombay on 11 July 1994 for a stop-over of approx. 48 hrs. Schedule departure time was 19:20, but, due to the late arrival of the inbound flight, KL874 departed 1:38 hr late. The crew had been notified about the delay beforehand in the hotel. After arrival at the airport, the cockpit crew, which consisted of the captain, first officer (F/O) and second officer (S/O), were briefed by the KLM operations officer. On this flight 1120 kg dry ice was to be loaded as refrigerant for vaccines. This amount of dry ice was above the limit stated in the Aircraft Operations Manual (AOM), but KLM Amsterdam had sent a telex, authorising this amount of dry ice on flight KL874. During the briefing it was noted that KLM Bombay had planned to load all cargo containing dry ice in the forward cargo hold of the aircraft, but the captain decided to distribute this cargo partly in the forward cargo hold and partly on the main deck cargo area. As a consequence of this (IATA) restricted cargo in the forward cargo hold, the temperature in this cargo hold must be set to a value, which require the airconditioning packs to operate in the partial high flow mode. This mode of operation requires an additional amount of fuel to be taken on board of 0.4% of the block fuel. Also, due to discrepancies between reported observed fuel indication and/or calculation, on this aircraft, 1% extra trip fuel had to be taken on board. During preflight planning both amounts of extra fuel were accounted for. Apart from the extra fuel, the flight plan fuel consisted of the trip fuel to destination, the minimum additional fuel (MAF) for 99% coverage, alternate fuel for Rotterdam Airport and taxi fuel. The MAF was calculated for 99% coverage due to the weather forecast for destination Amsterdam, which indicated a visibility of 4000 m. The alternate fuel for Rotterdam Airport included 30 minutes final reserve. The total amount of fuel to be tanked was calculated to be 99.550 kg. Flight KL874 was to be executed during night time hours and on this flight the F/O was to be the Pilot Flying (P/F) and the captain the Pilot Non Flying (PNF). Bombay ATC cleared KL874 to its destination Amsterdam via flight plan route and to maintain flight level (FL) 280 initially. The aircraft was pushed back from the gate at 20:53 and started to taxi at 20:58 for takeoff from runway 27. At that time, significant weather was situated over Bombay Airport, which produced a lot of rain, but the weather radar indicated that the departure route of KL874 over the Arabian Sea was relatively clear of clouds. However in view of the weather and the possibility of the existence of windshear, it was decided to make a take-off with full rated engine thrust. The aircraft became airborne at 21:09. After take-off the aircraft was operated with the right autopilot in command in the VNAV and HDG SLCT modes and with the autothrottle system engaged. The HDG SLCT mode was used to circumnavigate cumulonimbus clouds, which were visible on the weather radar. Acceleration to the initial climb speed and flap retraction was according schedule and uneventful, after which the after take-off checklist was performed. At 21:20, 11 minutes after take-off, while passing FL220 and climbing with an airspeed of approx. 330 kts, the flap position indicator became visible on the primary Engine Indicating and Crew Alerting System (EICAS). The flap position indicator changed to the expanded format a few seconds later and a FLAPS PRIMARY caution alert was triggered. At the same time the red maximum airspeed band on both Primary Flight Displays (PFD's) lowered to 260 kt and the yellow minimum airspeed band raised to 260 kts. The airspeed bands almost touched each other. The magenta speed command on both PFD's indicated 260 kts. It was noticed that the left band outboard leading edge group 1 (LH LE 1) flaps on the expanded flap position indicator showed an amber cross. Some time later the FLAPS PRIMARY alert on the primary EICAS changed to the FLAPS DRIVE caution alert. The emergency checklist (ECL) procedure was carried out and, in accordance with this procedure, it was attempted to obtain clearance from Bombay Air Traffic Control (ATC) to descend to a lower altitude (below FL200). The aircraft was initially levelled off at FL260 and the autothrottle was allowed to lower the airspeed to 260 kts. Shortly thereafter the aircraft climbed to FL280, as the crew was initially unable to contact Bombay ATC on high frequency (HF) radio for a reclearance to a lower altitude. After several attempts via HF radio and with the help of relay transmissions by other aircraft, clearance was obtained from Bombay ATC to descend to FL200. After the aircraft arrived at FL200, flying at an airspeed of approx. 255 kts, KLM movement control (AMS/LM) and KLM maintenance support (MSC) were contacted on HF radio. In concert with MSC it was decided to recycle the flaps, but after retracting the flaps, the same fault indication appeared on the primary EICAS. During visual inspection from the cabin, with the wing lights on, it could not be observed if the leading edge (LE) flaps were fully retracted. In this position the LE flaps are obscured from observation by the wings. However, it was observed that all LE flaps obtained their correct extended position. It was noticed that during extension of the flaps, the LH LE 1 flaps indicated green (normal extended position) much faster than the other flap groups. The LH LE 1 flaps indicated green in approx. 3 sec: while it took approx. 90 sec for the other LE flaps to indicate green. MSC then adviced the crew to retract the flaps by use of the alternate mode. This attempt was also unsuccessful. As a result of the observations during flap recycling, it was decided that most likely the fault indication was caused by a malfunction of a micro-switch, but it could not be excluded that the LH LE 1 flaps were (partly) extended and that therefore respected speed and altitude restrictions should be observed. However in concert with MSC, it was decided that the altitude restriction was not applicable (MSC contacted KLM operational engineering -SPL/OS- before advising KL874). By climbing to a higher altitude the range could be considerably extended and in concert with AMS/LM it was decided to continue the flight to a destination as close to Amsterdam as possible. The first suitable en route alternate was Dubai, but in order to land there, fuel had to be jettisoned, as the aircraft was still operating above its maximum landing weight. The aircraft climbed to FL240 and the Flight Management Computer (FMC) - operating in the speed limit (SPD LIM) mode - indicated 25.000 kg fuel remaining over Athens. It was therefore decided to continue the flight initially to Athens. Approx. 3 hrs after departure from Bombay, while flying at FL240, KL874 sent an Aircraft Communication Adressing and Reporting System (ACARS) message to AMS/LM, stating that, if the aircraft remained at FL240, they could reach Frankfurt with 5000 kg fuel remaining upon arrival. They also indicated that if KL874 could climb to FL390, the aircraft would be able to fly to Frankfurt with approx. 7000 kg fuel remaining upon landing. MSC responded to this ACARS message by stating, that they were anticipating to send a technical team and spare parts to Frankfurt and they requested the estimated time of arrival (ETA) for Frankfurt. The flight continued along its flight plan route and, after step climbs to FL260 and FL280, the aircraft climbed to FL390, approximately while passing abeam Amman. At that time the FMC indicated an ETA for Amsterdam of 07:05 with 4000 kg fuel remainin. This information was also passed on to AMS/LM via ACARS. KL874 indicated that if they were able to obtain full co-operation from ATC they would be able to reach Amsterdam, otherwise the aircraft would make an intermediate landing at Frankfurt. At time 03:39, approximately 3:30 hrs before landing at Amsterdam, the captain sent an ACARS message to AMS/LM requesting AMS/LM to contact the chief pilot to obtain permission to continue to Amsterdam and to land with 30 minutes fuel remaining. Some time later AMS/LM responded via ACARS that they had contacted the Schiphol Meteorological Office, Amsterdam ATC and the chief pilot. The meteorological office expected no specific weather problems at the time of expected landing of KL874, ATC indicated that they were willing to give priority to the flight and the chief pilot had stated that, in view of these facts, he had no objections if the aircraft would land at Schiphol with "30 plus" fuel remaining. During flight it was noticed that there was a large difference between the fuel totalizer indication on the ElCAS and the calculated fuel of the FMC. The totalizer indication on the EICAS was approximately 1200 kg lower than the FMC calculated fuel indication. The weather at Schiphol was monitored by the crew via ACARS and approaching Frankfurt the FMS had been programmed for a straight-in approach to runway 27 at Schiphol with a descent speed of 255 kts. At that time the FMC indicated approximately 5000 kg fuel remaining upon arrival at Schiphol. Taken into account the difference between the totalizer fuel indication and the FMC calculated fuel, the crew was, at that moment, convinced that they would land at Schiphol with at least 30 minutes reserve fuel (3830 kg). Based on the fact that the Schiphol Meteorological Office expected no weather problems, the fact that ATC would co-operate and the positive reaction of the chief pilot, shortly before Frankfurt, it was decided to continue the flight to its original destination Amsterdam. In close co-operation with ATC the crew expected the "fuel remaining" to increase, as was the previous trend, but after passing Frankfurt it was noted that the "fuel remaining" started to-decrease. The fuel totalizer on the EICAS indicated the same trend, albeit 1200 kg lower. Approaching top of descent, KL874 had to maintain altitude slightly longer than planned and instead of an uninterrupted straight-in descent and approach, KL874 was to maintain FL260 for approx. 1 minute, while ATC also instructed EL874 several times to fly diverging radar headings. Apparently other traffic (a Cathay Pacific B747 from Hong Kong also inbound for Amsterdam and flying along the same route) was conflicting with KL874, which was flying at a relatively low speed. Flying at FL260 the crew became convinced, that they would land with less than 30 minutes reserve fuel and requested from ATC a course direct to the Pampus VOR. Although KL874 did not actually declare a fuel emergency, they informed ATC that "otherwise they had to declare an emergency". After this statement, ATC cleared KL874 direct to the Pampus VOR for a straight-in ILS approach to runway 27. Passing approx. FL100 the EICAS fuel totalizer indicated 3900 kg and the EICAS alert FUEL QUANTITY LOW was triggered. The respective ECL procedure was performed and the crew briefing was expanded to cover the low fuel state of the aircraft. It was briefed that the aircraft was committed to land and an automatic landing would be made. Also, on suggestion of the S/O, the flaps were extended early in the approach, to make sure that they would operate normally. The aircraft landed at Amsterdam Schiphol Airport at 07:07. At touchdown the remaining totalizer fuel was approx. 2800 kg and the FMC calculated remaining fuel was approx. 4300 kg. After parking at the gate, after the engines were stopped, the fuel remaining indicated 2200 kg.

Injuries to persons

There were 240 passengers and 13 crew members on board the aircraft. There were no injuries among the passengers or crew.

Damage to the aircraft

There was no damage to the aircraft. After arrival at Schiphol, investigation revealed that the problem with the outboard LE Flap was caused by a damaged/shortened wire. After the wire was repaired, the LE Flap system was tested and found operating normal again

Note: In the incident follow-up report of the technical department it is stated, that this flap indication incident is regarded as an isolated case. However, it is known, that the same problem had occurred on 3 March 1992 with the PH-BFA, operating flight KL792 from Rio de Janeiro to Amsterdam.

Aircraft information

General

Aircraft type: Boeing 747- 406 Combi

Registration: PH-BFC

Serial number: 23982

Date of delivery: 01 sep 1989

Cert. of Airw.: No 39-73, valid until 29 nov 1994

Engines (4): General Electric CF6-80C2

Total hours: 21901

Total cycles: 3297

Weight and balance

The actual take-off weight of the aircraft was 331.937 kg and the take-off centre of gravity was at 26.3% Mean Aerodynamic Cord (MAC). The estimated landing weight was 235.500 kg with a landing centre of gravity of 28.1% MAC. The "dead load weight" centre of gravity (DLMAC) was 36.3% MAC. During flight the weight of the aircraft and the centre of gravity remained within certified limits.

Flight recorders

Data recorded on the UFDR is a sub-set of the data recorded on the ACMS. All data recorded on the ACMS was valid and for analysis purposes relevant parameters from the ACMS were used. No data from the UFDR was used for the investigation.

 

Meteorological information

Pre- flight weather information

The following weather information was presented to the crew during the pre-flight briefing at Bombay:

TERMINAL AREA FORECASTs (TAF):

VABB BOMBAY - FT 131600 1818 26010G20KT 2000 RA/DZ SCT015 SCT025 BKN100 BECMG 0406 26015G25KT BECMG 1416 26010G20KT TEMPO 1818 0800 SHRA BKN005 SCT030CB OVC080

EHAM AMSTERDAM - FT 131600 0018 32008KT 8000 NSC BECMG 0003 4000 BR SCT012 BKN100 PROB30 TEMPO 0108 34015G25 2000 TSRA SCT005 SCT030C8 BKN100 PROB30 0308 BKN005 BECMG 0710 35012KT 9999 NSW SCT020 BKN100

OMDB DUBAI - FT 131600 1818 18007KT CAVOK BECMG 0709 30013KT BECMG 1618 17006KT

LTBA ISTANBUL - FT 131600 1812 01013KT 9999 BKN035 PROB30 TEMPO 1821 6000 SHRA BKN030

EDDF FRANKFURT - FT 131600 0018 07007KT CAVOK PROB30 TEMPO 1218 23015G25KT 7000 TSRA BKN050CB

EDDL DUSSELDORF - FT 131600 0018 VRB03KT CAVOK TEMPO 0307 6000 BECMG 0810 SCT035 TEMPO 1018 26010G25KT 5000 TSRA BKN020CB

EBBR BRUSSELS - FT 131000 1812 27012KT CAVOK TEMPO 1824 5000 TSRA SCT030CB TEMPO 0306 5000 NSC

EHRD ROTTERDAM - FT 131600 0018 32008KT 8000 NSC BECMG 0003 4000 BR SCT012 BKN100 PROB30 TEMPO 0108 34015G25KT 2000 TSRA SCT005 SCT030CB BKN100 PROB30 0308 BKN005 BECMG 0710 35012KT 9999 NSW SCT020 BKN100

ACTUAL WEATHER REPORTs (METAR):

VABB BOMBAY - ATIS: 25010G20KT Temp 26 Q998

EHAM AMSTERDAM - SA 131825 33008KT CAVOK 20/16 Q1018 BECMG 7000

LTBA ISTANBUL - SA 131750 03008KT 9999 SCT035 25/18 Q1012 NOSIG

EDDF FRANKFURT - SA 131820 04005KT 350V130 CAVOK 29/11 Q1017 NOSIG

EDDL DUSSELDORF - SA 131820 07009KT CAVOK 28/15 Q1016 NOSIG

EBBR BRUSSELS - SA 131820 34009KT CAVOK 26/17 Q1018 NOSIG

EHRD RCTTERDAM - SA 131825 33007KT 310V010 9000 SHRA SCT042 SCT090 BKN120 21/16 Q1018NOSIG

SIGNIFICANT WEATHER INFORMATION (SIGMET):

EHAA 131448 WS SIGMET NR 1 VALID 131500/ 131800 EHAM. LINE OF ACT CB/TS ALONG W. BDRY OF AMSTERDAM FIR TOPS MAX FL320 MOV NNE 15-10KT INTST NC.

 

Weather information received during flight VIA ACARS:

2321 LGAT ATHENS - SA 132250 00000KT SCT025 22/19 Q1013 NOSIG

2321 EHAM AMSTERDAM - SA 132255 01004KT 310V050 4000 LN SCT100 BKN250 18/17 Q1018 NOSIG

2321 LGAT ATHENS - FT 132200 0624 VRB03KT CAVOK BECMG 0709 02014KT

2321 EHAM AMSTERDAM - FT 132200 0624 25005KT 4000 BR BKN015 BKN080 PROB40 0609 1800 BKN003 PROB30 TEMPO 0612 34015G25KT 2500 TSRA BKN025CB BECMG 0912 33012KT 9999 NSW SCT025 BKN040 PROB30 TEMPO 1218 6000 SHRA SCT025CB

0100 EDDF FRAMKFURT - FC 140000 0110 VRB03KT CAVOK

0100 EHAM AMSTERDAM - FC 140000 0110 33007KT 4000 BR NSC TEMPO 0110 34015G25KT 2500 TSRA SCT008 BKN025CB PROB40 0209 1800 BKN003

0323 EDDF FRANKFURT - SA 140250 05003KT CAVOK 19/15 Q1018 NOSIG

0323 EHAM AMSTERDAM - SA 140255 31004KT 3200 TSRA SCT003 OVC030CB 17/17 Q1019 RETSRA BECMG FM0330 NSW

0323 EDDL DUSSELDORF - SA 140250 36012KT 7000 TSRA SCT019 SCT040CB BKN070 19/17 Q1018 NOSIG

0324 EDDF FRANKFURT - FC 140000 0110 VRB03KT CAVOK

0324 EHAM AMSTERDAM - FC 140300 0413 35007KT 4000 BR NSC PROB30 TEMPO 0410 34015G25KT 2500 SHRA TSRA SCT008 BKN025CB PROB40 0509 1800 BKN003 BECMG 0912 33012KT 9999 NSW SCT025 BKN040

0324 EDDL DUSSELDORF - FC 140000 0110 14005KT CAVOK PROB30 TEMPO 0110 6000 TSRA BKN025CB

0502 EDDF FRANKFURT - SA 140450 02005KT CAVOK 19/17 Q1018 NOSIG

0502 EHAM AMSTERDAM - SA 140455 36005KT 320V030 6000 MIFG SCT003 BKN100 17/17 Q1018 RETSRA NOSIG

0502 EHRD ROTTERDAM - SA 140455 VR802KT 3500 SCTIOO BKN250 17/17 Q1018

0550 EDDF FRANKFURT - SA 140520 05003KT CAVOK 20117 Q1018 NOSIG

0550 EHAM AMSTERDAM - SA 140525 01006KT 6000 MIFG SCT060 BKNIOO 17/17 Q1018 NOSIG

0550 EHRD ROTTERDAM - SA 140525 33005KT 3000 BR SCT120 BKN160 17/17 Q1018 TEMPO 2500

0618 EDDF FRANKFURT - SA 140550 03001KT CAVOK 22117 Q1018 NOSIG

0620 EDDF FRANKFURT - SA 140550 03004KT CAVOK 22/17 Q1018 NOSIG

0620 EHAM AMSTERDAM - SA 140555 36004KT 320V030 2800 MIFG SCT005 SCT100 BKN150 18/18 Q1018 BKNO05

0620 EHRD ROTTERDAM - SA 140555 VRB02KT 2800 BR SCT120 SCT160 18/17 Q1018 BECMG ....

Note: Times stated above are the times (UTC) the ACARS message was received on board the aircraft

SCHIPHOL ATIS:

ARRIVAL ATIS "Lima" was active during the approach and landing of KL874:

LANDING RWY 06, TL40, EXIT NR 1 RWY 27 NOT AVAILABLE, ILS RWY 27 CAT 1 ONLY WIND 320 AT 6 KNOTS, VARIABLE BETWEEN 300 AND 050 DEGREES, VISIBILITY 2300 M, CLOUDS SCATTERED 500 FT, TEMPERATURE 18, DEWPOINT 18, QNH 1018 GRADU 500 FT BROKEN

Other information-flight plan

Flight KL874 was planned from Bombay to Amsterdam via overhead Dubai, Dhahran, Hilal, Banas, Mut, Istanbul and Linz. Initial planned cruising level was FL350. The en route alternate was Frankfurt and the filed alternate was Rotterdam. The Minimum Additional Fuel (MAF) was calculated with "99% coverage". Extra fuel was taken on board to account for observed fuel indication/calculation discrepancies (1% trip fuel for the PH-BFC) and 0.4% extra block fuel to account for partial pack high flow operation in the forward cargo hold.

Flight plan fuel calculation:

FUEL

Corrections

Endurance

88140

….

0830

Trip Incl 3% High Cons

2740

….

0021

99%Cov, 2Rwy:yes WX:no, ENRT ALT EDDF

6640

….

0050

Altn EHRD Plus 30 min Final Res

97520

….

0941

880

1280

….

Extra /(+ 0,4% ventilation hold 1&2)

98400

….

0941

TAKE-OFF

750

….

….

TAXI

99150

99550

0941

BLOCK

 

Actual fuel on board

According to the loadsheet, the take-off fuel was 98.800 kg. With 750 kg taxi fuel this would amount to 99.500 kg block fuel, which was in accordance with the flight plan. The flight plan fuel calculation was correctly performed. Based on the existing weather and Notice to Airmen (NOTAM) information it was decided to take Rotterdam Airport as 'close-by' alternate and Frankfurt as en route alternate. The weather forecast for Amsterdam indicated a visibility at arrival time of 4000 m, therefore the MAF had to be increased to 99% coverage. The extra fuel for indication/calculation discrepancies (880 kg, 1% trip fuel) was taken on board. Furthermore the extra fuel for partial pack high flow operation (400 kg) was also taken on board. NOTAM information received at Bombay contained no information which would require special attention.

Analysis

Departure

Departure from Bombay was uneventful although it was raining heavily at the departure time of KL874. During flight, existing thunderstorms could be avoided by use of the weather radar. After acceleration, initially a speed of 300 kt (Vb, turbulence speed) was maintained, but passing FL200, speed was increased to the standard climb speed (335 kts).

Flap indicating problem

Passing FL220, at an airspeed of approx. 330 kts, the EICAS alert FLAPS PRIMARY was triggered and the expanded flap position indicator was presented on the prim EICAS, indicating an amber cross through the LH LE 1 flaps, some time later followed by FLAPS DRIVE. The climb was initially stopped at FL260, but the aircraft was just out of range of Bombay ATC on very high frequency (VHF) radio and initially no contact could be established with Bombay ATC on HF frequencies. It was therefore decided to continue the climb to the first cleared en route flight level (FL280). If leading edge (LE) or trailing edge (TE) flap position data are invalid, an amber cross will appear inside the respective tape. This indication does not give any information about the actual position of the flaps, but merely indicates that the information reaching the computer is considered non-valid. In this case (as well as in the case of the incident with the PH-BFA on 3 March 1992), the FMC apparently "assumed" the LH LE group 1 flaps to be (partially) extended and consequently set the maximum airspeed limit to 260 kt (flaps 5 limit speed) and at the same time the autothrottle system reduced thrust to decrease the speed to the indicated maximum speed limit. Flaps should not be selected above 20.200 ft. For most operating conditions, the FMC calculates a speed envelope, based on relevant flight parameters. This speed envelope is presented to the pilots on their PFD, as the area between the top of the yellow minimum speed band and the lower side of the red maximum speed band. If flaps would be extended above 20.200 ft, and the aircraft is operating in the heavy weight bracket, this could lead to a situation where the minimum airspeed (based on 1.3 Vstall, Buffet Onset Boundary) is higher than the applicable maximum flap placard speed. According to information from the Boeing 747-400 Flight Management System (FMS) specifications, when no valid flap position is available both the active control minimum speed and the active control maximum speed are set to "No Computed Date (NCD) and zero and VNAV is unavailable, however (almost certainly) only TE flap position is taken into account. Consequently, in case of invalid LE flap position, the speed bands will remain in view, but it could not be established what speed limits would be indicated by the speed bands. The Emergency Checklist (ECL) procedure for FLAPS DRIVE states "maintain speed and configuration" and "do not exceed 20.000 ft". In order to fulfill these requirements, the autothrottle must be switched off, to maintain the applicable airspeed (for KL874 330 kts), after which the aircraft must descend to an altitude below 20.000 ft. The follow-up actions in the ECL the FLAPS DRIVE procedure provide only information for LE group indication 'solid amber', 'outlined amber' and 'striped amber'. In the relevant procedure no information is provided for LE group indication 'amber cross'. At the moment the incident occurred, the weight of th aircraft was 320.000 kg and the 1.3 Vstall speed was approx. 260 kt at FL260 and 262 kt at FL280. Therefor by allowing the autothrottle to reduce the airspeed to 260 kts, minimum and maximum airspeed could just be maintained. It has been established, that the aircraft remained within its operational limits and after clearance was received from Bombay ATC (via radio relay messages of other aircraft), KL874 descended to FL200.

Assistance from KLM Maintenance Support Centre (MSC)

After the aircraft reached FL200, contact was established, via HF radio, with MSC for technical advice. In concert with MSC it was decided to recycle the flaps. During recycling, visual observations were made from the cabin with the wing lights on, but it could not be established if the LE flaps were fully retracted. In the full retract position the LE flaps are obscured from observation from the cabin by the upper surface of the wings. It was, however, noticed that all LE flaps normally extended in the flaps 5 position, but after retracting the flaps the invalid indication on the EICAS returned. MSC then adviced to retract the flaps by use of the alternate mode. The crew was aware of the fact that the ECL procedure did stipulate not to use the alternate mode in case of a FLAPS DRIVE problem. The crew did query the advice of MSC, but was told to try to retract the flaps by use of the alternate mode anyway. After the attempt to retract the flaps in the alternate mode, the flap indication problem still persisted. The autopilot was disconnected for a short time, to verify that the aircraft was still flying "in trim" and that no actual asymmetric flap configuration existed. It was then decided that the flap indication problem was probably caused by malfunction of a micro-switch however, as it could not be established beyond any doubt that the flaps were fully retracted, the flap limit speed and altitude restrictions were adhered to.

Assistance from KLM Operational Engineerin (SPL/OS)

Posing an altitude restriction on the flight, considerably restricted the range and endurance of the flight in view of the existing amount of fuel on board. KL874 therefore requested permission to fly at a higher altitude. For this advice MSC contacted SPL/OS and they replied that the applicable speed limits should be adhered to, but that there were no restrictions to climb a higher altitude. SPL/OS based this advice on the fact, that the flap altitude restriction was only applied because no higher altitude for flap operation had been demonstrated. Flap operation is based on 10.000 ft above take-off an landing altitude. For Boeing 747 aircraft it is assume that the elevation of the highest airport is 10.200 ft hence the restriction for flap operation above 20.200 ft. It is felt that deviating from set limits should only be applied with utmost care, specifically as the operating crew might not be aware of the reasons behind an advice to deviate from these limitations.

Decision to continue the flight

It can be concluded that the crew handled the flap indication problem according the standard operating procedures (except for the attempt to retract the flaps by use of the alternate mode, on advice of MSQ and that the aircraft remained within the envelope of safe operation. The decision to continue the flight was correct, taken into account the advice from MSC and SPI/OS. Initially the range and endurance of KL874 were severely limited by the altitude restriction and therefore an intermediate landing at Dubai was considered. However the aircraft was still operating above its maximum landing weight and in order to make a landing in Dubai possible, fuel had to be jettisoned. While still flying at FL200, it was therefore decided to initially continue the flight to Athens. FMC fuel calculations indicated that the fuel remaining at Athens would be approx. 25.000 kg and the weather forecast of Athens, obtained via ACARS, indicated favourable weather. After "permission" from SPI/OS was obtained to climb to a higher altitude, further fuel calculations indicated that, if the flight could climb to FL390, a landing in Frankfurt would be possible, with 7000 kg fuel remaining. After pass abeam Amman, KL874 was cleared to climb to FL390 and based on the fuel calculations made, it was decided to continue the flight to Frankfurt.

KLM Basic Operations Manual (BOM)

According to BOM 2.4.2-1 (replanning), when a new destination is desirable, replanning should be done according to specific rules. In this case - replanning KL874 to Frankfurt - the rules for replanning a flight to a new destination without an alternate were applicable. Basically this rule states that the (planned) remaining fuel upon arrival should be adequate for 45 min of flight. Based on the flight plan of KL874, it was established that 45 min of flight amounted to 5750 kg fuel. On the flight plan of KL874 only a marginal fuel log was kept by the crew. Apparently part of the fuel calculations and checks, made by the crew, were made on another copy of the flight plan, which was discarded after the flight. Also, in the aircraft, there are only graphs and/or tables available for fuel calculations under normal conditions. If it is decided to continue the flight at a speed other than the standard cruise Mach number, fuel calculations can only be based on FMC calculations. However, the FMC does not take into account standard fuel planning margins. In order to establish the amount of fuel required to replan KL874 to Frankfurt, a test flightplan from Istanbul to Frankfurt has been made, for the same aircraft, with approximately the same weight. From this test flightplan it could be established, that KL874 could be replanned to Frankfurt without alternate according to the rules set forth in the KLM BOM. However before actually diverting to Frankfurt, it was decided to continue the flight to its original destination Amsterdam. The crew was of the opinion that they were allowed to plan the remainder of the flight in such a way, that they should arrive in Amsterdam with at least 30 min (3830 kg) fuel remaining. They based their opinion on BOM 2.4.2-3 (operating in the three phases), where it is stated that "the decision, either to continue the flight to the destination or to divert, shall be based on the planning of at least final reserve fuel as remaining fuel upon landing. Preferably final reserve + 15 minutes holding fuel should be planned as minimum remaining fuel upon landing". In this paragraph of the BOM no specific weather limits are stated. At the time the decision was made to continue the flight to Amsterdam, the forecasted visibility for Amsterdam was 4000 m at estimated arrival time, with a 30% probability of a temporary decrease to 2500 in. Apparently the crew had their doubts about the correct interpretation of the rules stated in the BOM and therefore they requested advice from the chief pilot via ACARS. The reply of the chief pilot, via ACARS indicated that "he had no objections against arrival in Amsterdam with 30 minutes arrival fuel". The crew interpreted this ACARS message as approval by the chief pilot to continue the flight to Amsterdam. The chief pilot later stated, that he had said to AMS/LM that he had no objection against '30 plus' minutes arrival fuel, whereby he indicated that he meant that the crew had to operate according to the BOM and that the final decision was their responsibility. Apart from the "advice" of the chief pilot, AMS/LM also indicated to the crew that the meteorological office at Schiphol expected no specific weather problems for landing and furthermore they had contacted ATC who indicated that they would co-operate with a straight-in arrival at Schiphol. At the time of decision, the crew was convinced that they would land at Schiphol with 30 minutes of fuel remaining. Together with the information received from AMS/LM, the decision was made to continue the flight to Amsterdam.

Advice from KLM Movement Control (AMS/LM)

AMS/LM stated per ACARS message, that "ATC would arrange priority". It should however be realized that this can never be interpreted as a watertight guarantee that full priority will be given by ATC upon arrival. Basically ATC can only guarantee an arrival with no undue delay, but normal traffic rules will still be applied. Only after an emergency has been declared, can ATC guarantee 100% priority. In this regard it should be mentioned that BOM 2.4.23 states that "when entering the abnormal (fuel) phase the captain shall consider a low fuel advisory to ATC". The terminology "low fuel advisory", however, is not defined in the BOM. Only in the KLM North Atlantic Regional Route Operations Manual (ROM) under USA SUMMARY - LOW FUEL ADVISORY is this terminology further used: "advice ATC of minimum fuel status, when fuel supply has reached a state where upon reaching destination undue delay cannot be accepted". In a note it is further stipulated that "this does not imply a need for traffic priority". It should be realized that the terminology "low fuel advisory" is a term only recognized in the USA. This terminology is not used by States which subscribe to the ICAO rules. It should be noted, that the ACARS message from AMS/LM, received at time 04:21 was stated in Dutch and during the investigation the F/O stated, that, being a non-Dutch speaking pilot, he had to consult the other pilots before he clearly understood the ACARS message from AMS/LM. Based on this discussion, he was of the opinion, that ATC guaranteed an unrestricted flight to Schiphol Airport.

Descent, approach and landing

Passing Frankfurt the calculated -remaining fuel on the FMC was approx. 5000 kg. Given the discrepancy in indication, the fuel totalizer indicated approx. 3800 kg, which was at that time barely enough for 30 min of flight (3830 kg). However, the crew expected the remaining fuel to increase, as they assumed full co-operation from ATC and priority during the last part of the flight. Contrary to their expectations, during the last part of the flight, before reaching top of descent (TOD), the remaining fuel decreased, initially to 4800 kg and then slowly to 4200 kg. At the moment the planned TOD was reached, KL874 did not get descent clearance, but instead had to maintain FL390 slightly longer and after descent clearance was obtained, the descent had to be stopped at FL260 for approx. 1 min. Apparently another B747, also inbound to Amsterdam, and flying along the same route as KL874, was the conflicting traffic. This aircraft was flying at a normal speed schedule, while KL874 was flying at a relatively low speed of 255 kts. Consequently the other B747 was overtaking KL874 and was given priority over KL874, according normal ATC rules. To obtain the required separation, KL874 was also given several diverging radar headings. KL874 had not indicated to ATC, that they were flying at a relatively low speed, neither had AMS/LM, when they contacted ATC for priority. While flying at FL260 it became apparent to the crew of KL874 that they would land at Schiphol with less than 30 min fuel remaining. At that moment KL874 informed ATC, that they required immediate clearance direct to the Pampus VOR, otherwise they had to declare a fuel emergency. ATC then cleared KL874 direct to Schiphol for a straight-in approach at runway 27 and vectored the other B747 behind KL874. Contrary to BOM 2.4.2-3 the captain did not formally declare a low fuel emergency. Although by "informing" ATC about the low fuel state, KL874 received priority clearance to Schiphol, ATC was not aware of the actual emergency situation and did not take any precautionary measures. Also ATC was not aware, that KL874 could not make a go-around. The KLM ROM very accurately describes the factors, which are applicable in such a condition. In the KLM ROM it is also clearly exIplained why, when and how an emergency should be declared. While passing FL100, during descent, the EICAS alert FUEL QUANT LOW was triggered and the crew of KL874 performed the relevant ECL procedure. On suggestion of the S/O the flaps were extended early in the approach to verify normal operation. This action, which was not planned, probably further decreased the amount of fuel remaining upon landing.

Fuel calculation

After arrival at the gate at Schiphol, it was observed that the FMC calculated remaining fuel indicated 2200 kg. It should be noted, however, that after arrival and after the engines are stopped, the FMC calculated remaining fuel is set equal to the totalizer fuel. As the fuel totalizer indicated approx. 1200 kg less (during descent this difference increased to approx. 1500 kg), it is most likely that the FMC calculated remaining fuel, after taxi to gate, was approx. 3700 kg. Totalizer fuel is recorded on the ACMS and the indicated totalizer fuel upon landing was 2800 kg. This would give a FMC calculated remaining fuel upon arrival of 4300 kg. At the time of the incident there was a known discrepancy between the FMC calculated fuel and the totalizer fuel. This discrepancy is known to the manufacturer and they are working on a solution. Tests indicate, that, when fuel quantity is low, the totalizer indicates in most cases a too low value, but this cannot be taken for granted. To cover for known discrepancies, an extra amount of fuel has to be taken on board and for fuel calculations the crew must use the lowest figures. It has been established, that the crew of KL874 was aware of this discrepancy and that they took the difference into account when they made the decision to continue the flight to Amsterdam. Nevertheless the crew expressed their surprise when they found out that the calculated remaining fuel became considerably less than what was expected after programming the FMC. Although the FMC was correctly programmed for an uninterrupted descent with an airspeed of 255 kts, it should be realized that the calculated fuel is based on the fuel flow for an aircraft in "clean" configuration. The amount of fuel calculated for the approach is a nominal value and any deviation from the "optimum" approach profile (e.g. early flap and/or gear extension, the use of speed brakes, etc.) would lead to the use more fuel, which is not covered in the FMC fuel calculations. The difference in expected and actual calculated fuel of approx. 1000 kg can therefore be explained in view of the non-optimum descent of KL874 and the early extension of the flaps. Shortly after arrival at the gate, the aircraft was refuelled. As a consequence the actual amount of fuel in the tanks could not be established.

Incident reporting

The incident came only to the attention of the flight safety department, after a trip report from the captain, regarding the low fuel state upon arrival, was received. Fuel remaining does not form part of the regular "flight data exceedance" program. Also, because no formal emergency was declared, AMS/LM did not inform relevant departments about the incident of KL874.

Conclusions

Findings

  • The aircraft had a valid Certificate of Airworthiness and a valid Maintenance Certificate.

  • The operating crew was properly licensed and adequately experienced to conduct the flight.

  • The pre-flight planning wag correct and the total amount of fuel taken on board was according the KLM fuel policy.

  • After the LE flap indication problem occurred, the crew acted according standard operating procedures and the speed of the aircraft was kept within safe operational margins.

  • The advice of MSC, to retract the flaps by use of the alternate mode, was contrary to standard operating procedures and was not correct.

  • The advice of SPL/OS, that the climb restriction stated in the standard operating procedure, could be disregarded, was based on personal knowledge and was not substantiated by the KLM Aircraft Operations Manual or the Boeing Aircraft Flight Manual.

  • Based on the advice, given by MSC and SPL/OS, the crew was justified in their decision to continue the flight.

  • The decision of the crew to continue the flight to Frankfurt, based on at least 45 min fuel remaining upon arrival, was in accordance with the rules set forth in the KLM BOM.

  • Although not explicitly stated in the KLM BOM, the decision of the crew to continue the flight to its original destination Amsterdam, should have been based on the rules for "in-flight" replanning and not according to the rules set forth for diversion to the (planned) alternate.

  • The rules in the KLM BOM 2.4.2, regarding "Fuel Policy and Tanking" are not unambiguous. In-flight replanning to original destination without alternate is not covered by these rules.

  • The advice, given by AMS/LM, that the flight would be given priority by ATC, is not supported by ICAO rules.

  • The advice of the chief pilot, that he had no objections to arrival of the flight in Amsterdam with "30-plus" fuel, was confusing and consequently misinterpreted by the crew. Furthermore this advice was not correctly relayed by AMS/LM to the crew of KL874.

  • During descent, when the crew was convinced that they would land with less than 30 min fuel remaining upon landing, an emergency (either by use of a "PAN-call" or a "MAYDAY-call") should have been declared.

Causal factors

  • The waiver of the altitude restriction started a decision making process in the cockpit, which could be defined as "decisions, being continuously post poned".

  • The decision making process was characterized as being too much "company-minded". This process was further stimulated by responses from AMS/LM and MSC, in which possible opportunities were taken for granted.

  • The fuel policy, as stated in the KLM BOM, is ambiguous and leaves too much room for interpretation.

  • Fuel calculations for replanning can only be made by reference to FMC calculations. There are no other data sources available in the cockpit of the aircraft to check the FMC fuel calculations.

  • While using fuel calculations made by the FMC, planning margins were not taken into account.

  • The advice from AMS/LM that "priority would be arranged" was incorrectly interpretated as a solid guarantee for an optimum flight path to destination Schiphol.

  • The decision to continue the flight to Amsterdam, with only 30 min fuel remaining upon landing, was based on programming the FMC for an optimum flight path without room for any deviation.

Recommendations

  • KLM Maintenance Support should be made aware, that technical advice to aircraft in flight might be restricted by standard operating procedures.

  • In respective manuals, attention should be given to the possibility that the FMC may calculate and present data, based on non-valid inputs. General guidelines should be provided, how to operate the aircraft under these circumstances.

  • A procedure should be made for the Boeing 747-400 for LE flap indication 'amber cross'.

  • For aircraft, equipped with EFIS cockpit technology, more information should be provided regarding the possibilities and the restrictions of fuel calculations made by the FMC.

  • Inform KLM Movement Control that it is not possible to obtain "solid" guarantees from ATC for priority handling. Relevant ICA0 rules should be clear.

  • All ACARS messages, related to the operation of the aircraft, should be made in the English language.

  • The terminology "low fuel advisory" in the KLM BOM (and KLM ROM) should be defined and further expanded in accordance with ICAO rules.

  • The fuel policy as stated in the KLM BOM should be updated in such a way that replanning to the original destination without alternate will also be covered by this policy.

  • The findings of this investigation should be published among all KLM pilots and flight engineers.

Incident Final Report status

Serious incidents have to be reported by KLM to the Dutch CAA (RLD). It is then decided whether an investigation will take place and who will perform the investigation. Normally the investigation will be conducted by KLM under supervision of the RLD. If SPL/OI (Flight Safety & Quality Assurance) has been assigned the task for the investigation, it must be assured that the investigation will be independent and impartial. The investigation will be concluded by the publication of a final report, which will be presented to all parties involved. The contents of the final report is the responsibility of SPL/OI and does not necessarily reflect the opinion of the RLD or Management KLM Flight Operations. After publication of the final report, Management KLM Flight Operations will discuss the report and will then decide upon the recommendations issued in the report.

 

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