On 1 August 2014 a Qantas Boeing 737-838 aircraft (registered VH-VZR and operated as QF842) commenced take-off from Sydney Airport, New South Wales. The flight was a scheduled passenger service from Sydney to Darwin, Northern Territory.
While the aircraft was climbing to cruise level, a cabin crew member reported hearing a ‘squeak’ during rotation. Suspecting a tailstrike, the flight crew conducted the tailstrike checklist and contacted the operator’s maintenance support. With no indication of a tailstrike, they continued to Darwin and landed normally.
After landing, the captain noticed some paint was scraped off the protective tailskid. This indicated the aircraft’s tail only just contacted the ground during take-off.
The ATSB found the tailstrike was the result of two independent and inadvertent data entry errors in calculating the take-off performance data. As a result, the take-off weight used was 10 tonne lower than the actual weight. This resulted in the take-off speeds and engine thrust setting calculated and used for the take-off being too low. As a result, when the aircraft was rotated, it overpitched and contacted the runway.
The ATSB also identified that the Qantas procedure for conducting a check of the Vref40 speed could be misinterpreted. This negated the effectiveness of that check as a defence for identifying data entry errors.
Qantas has advised that, in response to this occurrence, the Central Display Unit pre-flight procedure has been modified. This modification requires that, after the take-off data has been compared/verified by both flight crew, they are to check the ‘APPROACH REF’ page and verify the Vref40 speed.
In addition, Qantas also advised that the Flight Crew Operating Manual was amended to include a check that the take-off weight in the flight management computer matched that from the final loadsheet. This check was also to ensure the take-off weight from the final loadsheet was not greater than that used for calculating the take-off performance data.
Data input errors can occur irrespective of pilot experience, operator, aircraft type, location or take-off performance calculation method.
Effective management and systems can significantly reduce the risk of data input errors. Good communication and independent cross-checks between pilots, effective operating procedures, improved aircraft automation systems and software design, and clear and complete flight documentation will all help prevent or uncover data entry errors.
The application of correct operating data is a foundational and critical element of flight safety, but errors in the calculation, entry and checking of data are not uncommon.