Investigation into Jet Airways B777 VT-JEK Serious Incident at Heathrow
On 30 August 2016 Jet Airways Boeing B777-300 VT-JEK departed from Runway 27L at London Heathrow bound for Mumbai with 231 passengers and 15 crew on board. The aircraft departed from intersection departure S4E rather than using the full length of the runway and radio altimeter data showed the aircraft a height above ground of 16 feet at the end of the runway and at 112 feet at the airport perimeter road.
The investigation was delegated by the UK Air Accidents Investigation Branch (UK AAIB) to the Indian Aircraft Accident Investigation Bureau (AAIB). Their safety investigation report was published on 10 August 2018.
History of the Flight
At the time taxiway works mean that an aircraft from Terminal 4, on the south side of Heathrow, would have to cross Runway 27L at S4E, then taxi East, in order to access the full length of 27L.
Air traffic asked in the aircraft needed the full length, to which the pilot replied “Negative, S4 acceptable”. The AAIB say that:
As the aircraft passed the end of the runway, the three radio altimeters recorded heights above the surface of 16.4 ft, 16.6 ft and 17 ft respectively.
Before the flight the co-pilot had done an initial performance calculation with the aircraft’s Electronic Flight Bag (EFB) Onboard Performance Tool (OPT) that showed take-off from S4E would be acceptable. This was then repeated by both crew members when the actual, higher, take off mass was confirmed. The Captain however entered departure from the “First 4″ (Northern) intersections to 27L not S4E. The calculations therefore didn’t agree, until the co-pilot also selected the same erroneous intersections as the Captain.
The aircraft therefore took off with a lower thrust than needed.
A Boeing analysis for the AAIB found that the takeoff distance required to meet regulatory requirements was 3349 m whereas the takeoff distance available from intersection S4E was 2589 m. So while the aircraft lifted off, it:
- Did not meet regulatory requirements for the all-engine, continued takeoff case.
- Would not have been able to reject the takeoff and stop in the runway remaining following an engine failure just below V1.
- Would not have been able to continue the takeoff while meeting regulatory requirements following an engine failure just above V1.
AAIB note that:
From a procedural perspective, there appeared to be no assurance that an incorrect or invalid entry into the OPT made at the departure briefing would be corrected before the performance calculation was made.
Company SOPs separated the calculation of aircraft takeoff performance into two discrete procedures without an explicit check that data entered during the first procedure (the departure briefing) was still valid and appropriate during the second (after receipt of the load sheet).
The operator confirmed that, after the crew selected FIRST 4 on the OPT, although four performance solutions were available corresponding to the first four intersections, the default output was used to programme the CDU for departure. The default output provided performance information for a departure from N1 (Runway 27L full length).
The operator reviewed its SOPs and concluded that they did not trap data input errors e.g. using the incorrect runway intersection or environmental conditions, or selecting the incorrect thrust de-rate. It issued SOP Revision 1 on 1 st September 2016 to address these deficiencies.
Five safety recommendations were raised.
Besides the insufficient thrust setting, the calculated take-off speeds were invalid. In both incidents the required safety margins for take-off performance were not met, increasing the risk of a runway overrun, tail strike and a collision with an obstacle after departure. During the first serious incident (2014) the operator made use of manual performance calculations, whilst the second serious incident (2015) occurred after the operator had introduced digital performance calculations on an EFB.
While calculating takeoff performance data, the flight crew elected to use the Multiple Runway Computation (MRC) function on their EFB. Due to a software anomaly in the EFB, runway information for Runway 31 was displayed alongside takeoff performance data for Runway 13. The flight crew did not notice this during cross‑checking and subsequently took off from Runway 31 using takeoff performance figures for Runway 13.
The manufacturer (of both the aircraft and the EFB), operator and flight crew were unaware of this anomaly at the time of the serious incident. The operator has since disabled this function in the EFB and the manufacturer has communicated this anomaly to all affected operators of this version of the EFB.
In another UK case:
The flight crew planned to perform a takeoff from Runway 25 using Intersection Bravo at Belfast Aldergrove Airport. The initial performance figures, calculated using the EFB, were computed for a wet runway; this produced a full power thrust setting. Just before pushback, as the runway was dry, the crew elected to change the runway state on the EFB from wet to dry to see if this would produce a reduced engine thrust setting, which it did.
During the takeoff roll, as the end of the runway became visible at about 115 kt, the commander felt that a rejected takeoff would not provide sufficient stopping distance and thus became ‘Go’ minded. The aircraft subsequently got airborne with about 200 m of runway remaining.
After departure, analysis by the crew revealed that an incorrect runway was used to calculate the dry runway performance figures, resulting in erroneous figures being generated. The reason for this could not be confirmed but subsequent investigations revealed that in one scenario, an involuntary runway change could occur on the EFB. This anomaly was not known by the operator or manufacturer at the time of the event and is likely to have been the reason for the incorrect runway selection. These figures were not identified as erroneous and were subsequently used for takeoff.
On 21 July 2017 at 1539 hrs, C-FWGH took off from Belfast International Airport with a thrust setting which was significantly below that required for the conditions of the day. Preliminary evidence indicated that, after the aircraft lifted off from the runway, one of the aircraft tyres struck a runway approach light, which was 35 cm high and 29 m beyond the end of the runway.
The N1 required to achieve the required takeoff performance was 93.3% but 81.5% was used instead. Independent assessments by the AAIB and operator showed that the only credible way for this to have happened was for an error to have been made whilst entering the OAT into the FMC. If the top-of-climb OAT was mistakenly inserted into the OAT field on the n1 limit page (a figure of -52°C as opposed to +16°C), and the correct assumed temperature of 48°C was entered, the FMC would have calculated a target takeoff N1 of 81.5%. The investigation will consider how such a data entry error could have been made, and whether actual aircraft performance matched that which would be expected given the N1 power setting used.
The Australian Transport Safety Bureau (ATSB) research report Take-off performance calculation and entry errors: A global perspective concluded that despite advanced aircraft systems and robust operating procedures, accidents continue to occur during the take-off phase of flight.
Data errors, such as the wrong figure being used as well as data being entered incorrectly, not being updated, or being excluded, happen for many different reasons. The ATSB web page Data input errors highlights that no one is immune from data input errors.
However, risk can be significantly reduced through effective management and systems.
It is imperative that the aviation industry continues to explore solutions to firstly minimise the opportunities for take-off performance parameter errors from occurring and secondly, maximise the chance that any errors that do occur are detected and/or do not lead to negative consequences.