UK investigators have revealed that a weight entry error during take-off calculations resulted in a Blue Air Boeing 737-800's suffering a tail-strike on departure from Birmingham.
Analysis of the incident, on 28 July last year, found that the captain read the zero-fuel weight – rather than the take-off weight – to the first officer during calculations for take-off performance.
This incorrect weight, 12t below the actual figure, was entered into the electronic flightbag.
The flight was nearly 1h behind schedule for its service to Bucharest and the crew had been assigned a specific calculated take-off time from air traffic control.
"It was likely that the incorrect weight was read out, and not crosschecked, as the crew tried to meet [this take-off slot]," says the UK Air Accidents Investigation Branch.
The error meant the critical take-off speeds calculated were more than 10kt below that required for the aircraft's condition. These included a rotation speed of 140kt which should have been 153kt.
As the aircraft rotated from runway 15 at 143kt, ground operations personnel saw the tail of the jet come close to the ground and air traffic control asked the crew whether they had experienced a strike.
The 737 pitched almost 12° nose-up as it lifted off, above the tail-strike threshold of 11°.
Although the pilots did not believe the jet had struck the ground, they discovered the flightbag error and were also informed by aft cabin crew of an odd noise on take-off.
Despite these findings the crew opted not to consult the quick-reference handbook and instead proceeded to Bucharest.
"Continuing to destination put the safety of the aircraft and its occupants at an increased risk," says the inquiry.
Inspection of the 737 after it landed showed damage to the tail-skid and auxiliary power unit drain mast. None of the 190 passengers and six crew members was injured.