Tanik Mahmud died mysteriously aboard an RAF Chinook helicopter.

Twin-engine choppers ... two Chinooks are visiting Canberra on their way to Townsville.

After mysterious helicopters woke Canberrans through the nights last week, a couple of much larger visitors have thumped through the capital's skies this afternoon.

For those wondering what today's airborne lunchtime racket was all about, a Department of Defence spokeswoman has confirmed that there are two Chinooks currently visiting the ACT.

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The pair of twin-engine, tandem rotor heavy-lift helicopters are on their way from South Australia to Townsville, and are spending the night at Fairbairn Airforce Base tonight.

They could be heard flying over the capital around midday today, seemingly passing over parts of the city more than once.

The Boeing CH-47 is a huge aircraft used by the army for troop movement, artillery emplacement and battlefield re-supply. The 10 tonne helicopters can carry up to 33 passengers or lift up to 11 tonnes in cargo, and reach speeds of 170 knots (315km/h).

The Defence spokeswoman was not aware of any specific exercises scheduled, however said it was possible some training could have been taking place over the capital city today.