A Qantas Boeing 737 flight from Canberra to Perth had a “nose-heavy” take-off after more than half of the passengers were assigned the incorrect weight.

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The Australian Transport Safety Bureau (ATSB) said in a report released on Wednesday that the 87 primary school children on the May 9 flight had all been assigned the standard adult weight of 87kg during check-in.

The flight was also carrying 63 adult passengers and crew.

With the children seated together at the rear of the cabin, the aircraft appeared nose-heavy during take-off, forcing the captain to apply significant back pressure to achieve lift off from the runway.

Too much back pressure could have caused the aircraft tail to strike the runway, but the captain managed to ease the aircraft into the air.

It was subsequently determined that the final load sheet overstated the aircraft take-off weight by about 3.5 to five tonnes.

The ATSB said Qantas had issued a new procedure notification to check-in staff, reminding them to ensure that when a group movement advice referred to children, they must also be accepted in the customer management system as children.