Flap and landing gear overspeed highlights need to crosscheck and validate take-off speed calculations

Generic A320 flightdeck

Incorrectly calculated take-off speeds contributed to an Airbus A320 experiencing a flap and landing gear retraction overspeed events, an ATSB investigation has established.

While preparing for a flight from Sydney to Melbourne, the flight crew of the Jetstar Airways A320 were unable to use two electronic flight bags to calculate and check take-off performance data, and instead used manual take-off charts.

But the flight crew inadvertently calculated speeds that were higher than required for the actual aircraft weight and environmental conditions, and those incorrect take-off speeds were not identified by independent verification and cross-checking.

Consequently, the aircraft did not rotate to the correct pitch attitude during its take-off roll, resulting in a higher acceleration rate than anticipated. As a result, the aircraft’s speed at rotation was only 16 knots below the maximum flap extended speed.

Following rotation, the pitch rate remained under the recommended rate, and continued to reduce with the aircraft’s speed increasing. The pilot flying was not alerted to the incorrect pitch attitude rotation; however the pilot monitoring called ‘speed, speed’ to assist in the management of airspeed. The flap extended limit speed was exceeded five seconds after rotation.

This incident highlights the importance of independent validation and crosscheck of flight performance data, in particular performance speeds and aircraft weight.

When alerted to the impending overspeed, the pilot flying reduced the engine power in response, rather than increasing the aircraft pitch. The action of reducing the engine power was taken when the aircraft was below the safe altitude above ground.

Then, climbing through 2,800 feet, the flight crew reported hearing a buffeting noise, and they soon determined that the landing gear was still extended. The pilot flying immediately called ‘gear up’ and the pilot monitoring quickly retracted the landing gear without looking at the speed indication, which was 30 knots above the maximum landing gear retraction speed.

The flight crew discussed the occurrence and with no known adverse indications, they continued the flight to Melbourne without further incident.

“This incident highlights the importance of independent validation and cross-check of flight performance data, in particular performance speeds and aircraft weight,” ATSB Transport Safety Director Dr Stuart Godley said.

The ATSB found that when using the manual take-off charts, the procedure for the calculation for the correct take-off performance speed for the aircraft’s actual total take-off weight was not completed, resulting in a calculated rotation speed based on an aircraft weight significantly heavier than their actual take-off weight.

“This error was not detected through an independent validation crosscheck,” Dr Godley said.

“This investigation emphasises the importance of considering reasonability and accuracy checks, consulting company procedures manuals in the event of electronic flight bag issues, and conducting a normal rotation followed by reference to the Speed Reference System,” Dr Godley said.

You can find here the report AO-2018-067: Incorrect configuration involving an Airbus A320, VH-VFX, Sydney, New South Wales, on 29 September 2019

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