In August of last year, a Boeing 737-838 airplane that was flown by Australian airline Qantas had a “tailstrike” incident when taking off from Sydney Airport. A tailstrike is when the rear of the plane hits the ground in a hard fashion as it is thrusting upwards. Recently, the Australian Transport Safety Bureau determined that the tailstrike was caused by a miscalculation of the plane’s takeoff weight.
When the pilot went to put the weight into the takeoff calculation, he put in 66,400 kg instead of 76,400. This error caused the plane to lack enough power to clear the runway without first clipping the pavement with its tail. The calculation was performed using an iPad that was in no way connected to the plane. There was no software glitch, and there was nothing wrong with the airplane. It was just a routine case of human error.
Because of this error, the engine thrust was set too low. Thrust was set to 88.4%, and the takeoff speed was 146 knots. With the correct weight, thrust would have been set to 93.1% with a takeoff speed of 157 knots. The higher values would have been able to get the plane safely off the ground.
Interestingly, neither the pilot nor co-pilot recognized the low value they input into the calculation, even though they both had more than 10,000 hours of flying experience at the time. Still, with the amount of variables that they have to input, it’s not much of a surprise that they missed this detail. Additionally, thrust and takeoff speeds can both greatly vary from flight to flight, and the numbers they came up with were within reason. That’s most likely why they didn’t question anything.
Fortunately, the tailstrike was very minor. Other than some paint that had been scraped off, the plane was completely fine. However, other tailstrikes have proven to be deadly. In 1985, the damage from a previously unnoticed tailstrike on a Japanese flight of a Boeing 747 led to the deaths of 520 people when the plane exploded because of decompression.
Since the most recent incident, Qantas has altered its launching procedures to prevent a future tailstrike. The pilot and co-pilot now do separate calculations, and they are required to double-check the plane’s intended takeoff speed in the reference manual.