Transavia B738 at Groningen on Sep 18th 2014, insufficient takeoff performance

Last Update: March 13, 2018 / 22:39:06 GMT/Zulu time

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Incident Facts

Date of incident
Sep 18, 2014

Classification
Report

Flight number
HV-143

Aircraft Registration
PH-HZD

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Transavia Boeing 737-800, registration PH-HZD performing flight HV-143 from Groningen to Rotterdam (Netherlands) with 173 passengers and 6 crew, lined up Groningen's runway 05 at intersection S3 and was accelerating for takeoff with the captain being pilot flying when the captain noticed above 80 knots that the acceleration was not as expected. The captain assessed that insufficient runway was available to reject takeoff and continued the takeoff. The first officer suggested to rotate early, the captain rotated the aircraft at Vr, the aircraft became airborne 60 meters/200 feet short of the runway end. The flight continued to Rotterdam 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 Lisbon, see Report: Transavia B738 at Lisbon on Dec 3rd 2015, 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 Groningen incident, the insufficient thrust setting was the consequence of a miscalculation on the bugcard.

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 to the calculation error in the Groningen incident were:

- the large number of calculations, data entries and data transfers;

- the lack of guidelines regarding which source should be used for the weight in the take-off performance calculation.

- lack of guidelines regarding the purpose of the bugcard, leading to it being used for a calculation whilst it is meant solely as a reference chart.

The DSB analysed:

The performance calculation was based on a TOW that was 10 t lower than the actual TOW of 62.9 t and a wind component of 0 kt. The actual take-off thrust, resulting from the performance calculation, was therefore less than the required take-off thrust setting. As a consequence none of the required safety margins were met. An engine failure at V1 would have resulted in a runway excursion. Even without an engine failure, the available runway length was 68 m too short for the required take-off run distance according to aircraft manufacturer Boeing. Boeing calculated the take-off distances for the same thrust setting and conditions as the incident flight. The fact that the aircraft became airborne approximately 60 m before the end of the runway can be attributed to the fact that these calculations use conservative assumptions.

The take-off speeds were calculated for the correct take-off weight as they were derived from the FMC, which was programmed with the correct weight figures. However, the erroneous assumed temperature of 60 degrees Celsius was also programmed into the FMC.

From the pilots perspective intersection S3 of runway 05 was a valid choice for take-off. Their performance calculation, using the erroneous 10 t low takeoff weight, showed that both a take-off from the beginning of the runway and from the intersection were possible with the same thrust reduction. Taking-off from the intersection saved time and improved the flow of traffic, as no back track was required on the runway.

The weight used for the performance calculation was the weight as written on the bugcard, which was 52,9 t. Performance penalties for the use of bleed air and a lower than standard QNH were correctly applied to this weight. Hence, the weight used in the performance tables was 55,5 t. The flight crew used the zero wind column in the performance tables to find the maximum assumed temperature at which the engines would provide sufficient thrust for a safe takeoff. This showed a temperature of 60 degrees Celsius, which was the maximum temperature noted in the performance tables. When entering the performance tables with the correct takeoff weight, adjusted for performance penalties to 65,5 t, the tables show an assumed temperature of 30 degrees Celsius. The thrust setting corresponding to an assumed temperature of 30 degrees Celsius is significantly higher than the thrust setting corresponding to an assumed temperature of 60 degrees Celsius and would have been sufficient for a safe takeoff in windless conditions.

The wind, according to the ATIS, was from direction 100 degrees with a steady component of 5 kt, but variable in direction between 060 and 170 degrees and variable in wind speed between 3 and 11 kt. This means that wind from direction 170 degrees with a speed of 11 kt was possible. As runway 05 was in use there was a possibility of a 120 degree angle between the runway heading and the wind direction. At a wind speed of 11 kt this would create a tailwind component of 5,5 kt. Entering the performance tables for a 5 kt tailwind component and the erroneous 55,5 t takeoff weight shows a maximum assumed temperature of 52 degrees Celsius. When entering the performance tables for a 5 kt tailwind and the correct weight of 65,5 t, the performance tables show a temperature of 8 degrees Celsius. As the outside air temperature was 24 degrees Celsius, a takeoff would then not have been possible from intersection S3. A takeoff from the beginning of runway 05 would then have been required. The operator’s performance manual does not accurately describe which wind direction and speed should be taken into account in case of a variable wind direction and speed.

The ACMS take-off data (Appendix C, Figure 1) shows that groundspeed and calibrated airspeed during the take-off roll were the same, or that calibrated airspeed was higher, indicating no wind or headwind. Just before rotation, between 43 and 47 seconds into the event, the calibrated airspeed is lower than the groundspeed by approximately 4 kt. This indicates tailwind. Although this period is short, a tailwind does negatively influence the performance of the aircraft. The effect of the short period of tailwind however, is minor compared to the effect of the erroneous take-off weight used for the performance calculation.

Contributing factors to the calculation error

Although the bugcard is not designed as a chart on which calculations are to be completed, there is no description of the exact purpose of the bugcard as a reference chart on which only results of calculations are to be noted in the manuals of the operator. The TOW on the bugcard can be calculated by adding the take-off fuel weight to the ZFW33 or can be transferred directly from the LTS. Choosing to make a TOW calculation on the bugcard is unnecessary, as it has already been calculated on the LTS, and it presents an extra possibility to make a calculation error. Nevertheless this method could be used because of the lacking procedures describing the use of the bugcard. Furthermore, the FMC also displays the TOW after the ZFW as calculated on the LTS has been entered into the FMC. This value could also have been transferred onto the bugcard.

Neither the manuals (FCOM, FCTM), nor the operator, prescribe which TOW source should be used as the source for the performance calculation. In interviews the flight crew stated that pilots develop personal strategies with respect to which TOW is being used for the performance calculation. In this case the pilots used the incorrectly calculated TOW of 52.9 t from the bugcard as source for the performance calculation. Both pilots stated they were instructed to use the TOW from the bugcard for the performance calculation during their initial training with the operator.

Completing the weight and balance, performance calculation and FMC procedures required over twenty manual entries, data transfers and calculations to be performed by the flight crew. At each individual step there was a potential for making an error. The large number of steps, performed during the flight preparation process, increases the chance for errors.

No indications have been found that flight crew fatigue has been a contributing factor in the calculation error.
Aircraft Registration Data
Registration mark
PH-HZD
Country of Registration
Netherlands
Date of Registration
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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
Sep 18, 2014

Classification
Report

Flight number
HV-143

Aircraft Registration
PH-HZD

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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