On the 1st of August, 2014, cabin crew aboard a 737 operated by Australian airline QANTAS reported hearing a “squeak” during takeoff. The crew's ears were good: the sound they heard was the plane's tail scraping the ground – a “tailstrike” - during takeoff.

That's the conclusion of an Australian Transport Safety Bureau (ATSB) investigation into QF842, a QANTAS flight between Sydney and Darwin.

So how did this one happen? Data entry has been – pardon the pun – fingered as the cause of this incident because the plane's two pilots managed to make a “transposition error” by entering a takeoff weight of 66,400 kilograms when the correct value was 76,400 kilograms. The incorrect figure wasn't a surprise to the captain, who felt it was “not unusual and was consistent with recent sectors flown”.

Another typo, selecting an engine temperature of 51 degrees rather than the correct value of 35, saw the plane use less thrust than needed. The result of the two errors was “overpitch” – aviation cant for the plane taking off at a wrong angle, enough that the tail struck the ground.

“Kissed” the ground might be a better description because the “tailstrike” the crew heard was so slight that it did not trip a sensor carried specifically to detect such incidents. But the incident did light up an indicator in the plane's heads-up display that indicated tailstrike was possible.

The ATSB investigation suggests the data entry errors were inadvertent and that the crew were properly-rested, but that the “procedure for crew comparison of the calculated ... speed, while designed to assist in identifying a data entry error, could be misinterpreted, thereby negating the effectiveness of the check.”

It will come as no surprise to Reg readers to learn that planes aren't designed to drag their rears along runways, or that a plane with a damaged rear won't do well in the air. QF 842 avoided that problem, and hopefully also the fate that befell JAL 123 in 1985. That flight, a Boeing 747SR, caused 520 deaths when it struck a mountain after explosive decompression caused by faulty repairs following a tailstrike.

QANTAS has since adjusted its procedures so that both pilots verify the data entered into the airline's iPad app before takeoff. Watch your fingers, flyboys! ®