An ATSB investigation revealed that the crew of a Boeing 737-800 inadvertently used a too low takeoff weight in the on-board performance calculation, leading to a tailstrike during takeoff from Sydney.
The Boeing 737-838 aircraft, registered VH-VZR and operated by Qantas Airways as flight QF842, commenced take-off from runway 34L at Sydney Airport. The flight was a scheduled passenger service from Sydney to Darwin. The flight crew consisted of a captain, who was the pilot flying and a first officer, who was pilot monitoring. The flight crew reported gusty conditions for take-off. During the take-off, the aircraft was rotated at the calculated rotation speed of 146 kt. After the aircraft had reached FL110, the crew turned off the seatbelt sign. At this stage, they received a call from the cabin crewmember seated in the rear galley, reporting that they had heard a ‘squeak’ during the rotation. The flight crew levelled the airplane at FL280 to discuss the issue with the cabin crew and conduct the suspected tailstrike checklist. The captain was referencing the head-up guidance system (HGS) during the take-off and recalled seeing the ‘dumb bell’ symbol appear (which is the tailstrike pitch limit), however it did not appear to come into proximity of the aircraft reference symbol (which indicates the aircraft’s pitch).
After a discussion with the operator’s maintenance watch personnel, and given that the aircraft had pressurised normally and was not displaying any indications of a tailstrike or associated damage, the decision was made to continue the flight to Darwin. The flight progressed normally and landed in Darwin at about 1423 Central Standard Time.
After the passengers had disembarked, the captain conducted an inspection of the tail skid of the airplane and noticed some paint damage and scrape marks, however the cartridge containing the sensor for a tailstrike was still intact. This indicated that the tailskid had only just contacted the runway during the take-off. The captain phoned the operator’s duty captain to report the damage.
During a follow up phone call, the flight crew were asked to check the take-off performance figures calculated on their iPad and used to conduct the take-off in Sydney. During this check the first officer noted that the take-off weight entered into the on-board performance calculation tool on the iPad was incorrect and was 10 tonne lower than the actual take-off weight. The weight entered into the iPad tool was 66,400 kg instead of the actual weight of 76,400 kg. This resulted in the take-off speeds being calculated as V1 145 kt, VR 146 kt and V2 149 kt instead of V1 152 kt, VR 155 kt and V2 158 kt and a selected temperature of 51° instead of 35°. This reduced the take-off thrust setting from 93.1 per cent N1 RPM to 88.4 per cent. The lower speeds and higher temperature were subsequently entered into the aircraft’s flight management system and used for the take-off from Sydney.