Qantas Airways flight VH-VZR, a Boeing 737-838, scraped the runway when leaving Sydney airport on August 1 last year. The incident did not leave any major damage but still warranted an investigation by the Australian Transport Safety Bureau (ATSB).
Ars Technica reports that the bureau’s conclusion, released today, is the plane didn’t have enough thrust to clear the runway because the co-pilot had accidentally “fat-fingered” the keypad on his iPad’s screen. The airline uses the tablets to help with calculations made when preparing for launch.
According to the investigation, the co-pilot made a “transposition error” when inputting the plane’s takeoff weight, pressing 6 instead of 7. In other words, he entered 66,400kg instead of 76,400kg, reducing the plane’s weight by 10,000kg.
The co-pilot also made another mistake while providing the app with data, specifying the temperature as 51°C instead of 35°C. The report does not go into why this occurred. The incorrect measurements ultimately led to the plane taking off with 88.4 percent thrust at 146 knots. It should have lifted from the runway with thrust of 93.1 percent and speed of 157 knots.
The captain apparently didn’t question the measurements returned by the software because he had also got the plane’s weight wrong. While working it out independently on a notepad, he forgot to carry a “1” when adding up and also wrote down 66,400kg. The investigation noted that the software relies on so many variables that every result it produces can be very different, even when flying the same plane. Therefore, the crew cannot be expected to recognize a potentially incorrect value.
In this incident, the iPad was not directly at fault. The tablet is not connected to the plane and the software functioned as designed. As in so many other data input-related fails, a simple human error led to potentially disastrous consequences. The pilot and co-pilot involved both have over 10,000 hours of flying experience.
Thankfully, the trailstrike that occurred was very minor. A member of the cabin crew reported hearing a “squeak” during take-off and alerted the flight crew. They checked the plane’s sensors and contacted flight control, neither of which suggested a tailstrike had occurred. After landing the plane, the captain manually inspected the tail and found its paint had been scraped off.
Qantas has since tweaked its pre-flight procedures to ensure an incident similar to what happened in the cockpit of VH-VZR doesn’t happen again in the future. The pilot and co-pilot now have to consult the plane’s reference manual after individually working out the speed to take off at to see if their figure matches what is given as a guide by the manufacturer.
