Transavia B738 at Lisbon on Dec 3rd 2015, insufficient takeoff performance

Last Update: March 13, 2018 / 23:44:38 GMT/Zulu time

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Incident Facts

Date of incident
Dec 3, 2015

Classification
Report

Flight number
HV-5952

Aircraft Registration
PH-HSG

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Transavia Boeing 737-800, registration PH-HSG performing flight HV-5952 from Lisbon (Portugal) to Amsterdam (Netherlands) with 175 passengers and 6 crew, lined up Lisbon's runway 21 at intersection U5 and was accelerating for takeoff with the captain being pilot flying when both flight crew noticed just prior to V1 that their takeoff run was longer than expected. The crew continued takeoff, rotated at Vr and the aircraft became airborne 430 meters/1400 feet short of the runway end. The flight continued to Amsterdam for a safe landing without further incident.

The Dutch Safety Board released their final report in English and Dutch combining this occurrence as well as another occurrence in Groningen, see Report: Transavia B738 at Groningen on Sep 18th 2014, insufficient takeoff performance concluding:

In both incidents, the flight crew did not select additional thrust after realizing the take-off roll was longer than usual. Other investigation reports of performance incidents show that additional thrust is not selected in the majority of the cases. The selection of additional thrust during the take-off roll in performance incidents is not trained in flight simulators. This lack of training makes it less likely that flight crews select additional thrust in a time critical situation, such as a take-off made with an erroneous take-off performance calculation.

Direct causes

In the Lisbon incident an incorrect runway and take-off position selection in the EFB performance tool by the flight crew caused the insufficient thrust setting.

The errors could propagate because there were no adequate crosschecks in place to detect the errors. A crosscheck regarding the TOW on the bugcard was lacking in the Groningen incident.

Contributing factors of the selection error in the Lisbon incident were:

- the large number of data entries and transfers;

- the ergonomics of the EFB performance module;

- the ambiguous runway take-off position naming system at the airport.

- the large variation in take-off parameters due to the performance optimization of the EFB, which decreases the chance for flight crews to develop a feel for the values of take-off performance parameters.

The DSB analysed:

The aircraft departed from runway 21 position 3 (U5 intersection) as it was the preferred departure position with runway 21 in use. The runway length from this position was 2,410 m. This is sufficient for take-off with a Boeing 737-800 under normal conditions.

However, the take-off performance was erroneously calculated for a take-off from runway 03 position 3, from which the available TODA was 1120 m longer. As a consequence the available runway length was less than anticipated in the performance calculation and the subsequent thrust setting was not sufficient to meet the required safety margins. The fact that the remaining runway length at lift-off (430 m) was 211 m more than the calculated distance according to Boeing can be attributed to the fact that the calculations use conservative assumptions.

The runway selection error

In the EFB take-off performance module, both pilots inadvertently selected position 3 on the first page of the runway/identifier selection field. This was take-off position 3 of runway 03 instead of take-off position 3 of runway 21.

Runways often have multiple intersections available for take-off that pilots have to choose from. After selecting the correct runway, the identifier is the final criterion which determines the correct take-off position. The runway-identifier combination is a single selection in the EFB. At most airports the identifier field contains a unique character/ number combination (e.g. the runway intersection designator). Therefore it is likely that, in selecting the runway-identifier combination, the pilots in this case focused on the identifier instead of the runway number. Also, as was stated by one of the pilots, the layout of the selection window draws the focus to the identifier, as it clearly stands out with the blank spaces around the identifier. At Lisbon Airport, the runway identifiers were identical for both runway 03 and runway 21. There were a position 1, 2 and 3 for runway 03 as well as a position 1, 2 and 3 for runway 21. These positions marked different intersections. This made the flight crew susceptible to making a selection error.

The EFB displays the runway numbers and identifiers in a sequential order. As the selection field can only display a maximum of five runway-identifier combinations, the only PSN3 on this page was position 3 of runway 03. The pilots needed to scroll down to view the remaining options. As they saw the first PSN3 in the list, it is likely they thought that the this PSN was the correct one. In addition to this, pilots stated during interviews that runway 21 was rarely in use. Runway 03 was the runway both pilots usually landed and took off from at Lisbon Airport.

Contributing factors to the runway selection error

Take-off position identifiers

The EFB airport data file uses the airport data from the national AIP as source. Therefore the take-off position identifier names in the EFB were also ambiguous. Although ICAO Annex 14 Aerodromes does not provide requirements for the naming of take-off positions, most airports use a logical and unique naming system for aerodrome manoeuvring areas, such as taxiways and ramps.

The fact that the same position numbers are used for take-off positions on different runways in Lisbon increases the chance for errors, as proven by this incident and a previous incident with an Airbus A319.

During this investigation, Lisbon Airport changed the intersection names. The revised take-off intersection names are not conform the recommendations of the ACI Runway Safety Handbook. Furthermore, the revision of the take-off intersection names did not result in a unique naming of the take-off intersection positions. At present, a PSN M is available for runway 03 as well as runway 35. Therefore, there still is a potential for selecting the wrong runway in the take-off performance calculation in the EFB.

Fatigue

No indications have been found that fatigue has been a contributing factor in the calculation error.

EFB operation and workload

The EFB in use by the operator requires a number of manual data entries and data transfers, not only for operational, but also for administrative purposes. Pilots have to check, amongst others, crew data, flight sector data and aircraft data and make corrections where necessary. Passenger and load information has to be entered for the load and balance calculation. The input of airport and weather data is required for the take-off performance calculations. The data output has to be transferred to the bugcard and the FMC (see Figure 8 for a visualisation of the workflow).

Some information entered in the EFB is already available in the computer systems of the operator (e.g. catering information, flight type, additional equipment), however this information does not get automatically uploaded or transferred. The first officer stated during an interview that he often had to postpone non-essential tasks, which are of an administrative nature, until after take-off because of time pressure. This disrupts the regular workflow for which the EFB has been designed. The captain stated during an interview that because he had only recently been promoted to captain he felt susceptible to time pressure. The turn around time at Lisbon was scheduled to be 35 minutes. During a large portion of this time one member of the flight crew is required to be outside to supervise refuelling of the aircraft. This leaves only a short period of time where both pilots are on the flight deck doing preparations for the following flight.

Although the EFB reduces the number of calculations compared to the manual load and trim procedure (as in the Groningen incident), it still requires a large amount of manual data entries and data transfers. The operator is planning to incorporate a further integration of these functions in the next phase of the EFB, which will decrease the number of data entries.

Error propagation and crosschecking procedures

Crosschecking procedures

The main barrier against errors in the performance calculation is the crosscheck between the outcome of the two independent performance calculations as described in the FCOM and the FCTM, see paragraph 2.4.2. As both pilots made the same input error, the output was the same as well. For that reason the existing crosscheck on the output parameters was not adequate to detect this type of input error.

A small deviation in the input parameters, such as for instance the wind component, can make a substantial difference in the output. According to the flight crew, pilots tend to communicate the input parameters before entering them in the EFB to facilitate crosschecking at the end of the performance calculation. This increases the chance of common input errors being made and as such it reduces the effect of the crosscheck after completion of the performance calculation.

Once the performance calculation is completed, the performance module is closed and the EFB is used for different purposes. During taxi-out, the airport map or departure page of the Lido chart module is usually selected on the EFB. Due to the different software modules, the performance calculation results are not readily available during taxi as the EFB is then showing navigational charts. Therefore, it is not convenient for pilots to open the performance module for reference during taxi.

The EFB take-off performance calculation page incorporates a print button. However, in contrast to its name, the print button only stores the calculated data, it does not send any information to the onboard printer. A printed copy would make the performance calculation data readily available for crosschecking or reference purposes prior to take-off.

During the interviews the pilots mentioned that they have developed their own crosschecking strategy after the incident. This includes paying extra attention to the runway designator during the performance calculation process and a review of the performance data prior to take-off, including the runway/intersection used for the performance calculation. The manuals and procedures do not describe a particular crosscheck to this extent. The fact that pilots stated they developed their own crosschecking strategies when using the EFB is indicative that the existing company crosschecking strategies at the time of the incident were inadequate.

Experience and exposure

The EFB take-off performance calculation is not based on the concept of a balanced field take-off as used in the TL-tables and uses excess runway length for an improved climb performance whenever feasible. The software adjusts the decision speeds to achieve the maximum thrust reduction/maximum assumed temperature to conserve engine life. Under seemingly similar circumstances, the take-off configuration and or decision speeds can differ considerably. As a consequence pilot’s awareness and feel for numbers is reduced and a deviation from standard values will not easily be noticed. For instance, the awareness of the relation between the most relevant performance parameter values; TOW, thrust reduction, and TODA, is reduced.
Aircraft Registration Data
Registration mark
PH-HSG
Country of Registration
Netherlands
Date of Registration
Airworthyness Category
Legal Basis
Manufacturer
The Boeing Company
Aircraft Model / Type
737-800
ICAO Aircraft Type
B738
Year of Manufacture
Serial Number
Aircraft Address / Mode S Code (HEX)
Maximum Take off Mass (MTOM) [kg]
Engine Count
Engine
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Engine Type
Incident Facts

Date of incident
Dec 3, 2015

Classification
Report

Flight number
HV-5952

Aircraft Registration
PH-HSG

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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