Australian troops are flying into battle perched on Eskys in aging helicopters with a computer glitch that makes them violently stand on their nose - a flaw already blamed for killing one Digger and injuring five others.
Expert evidence to a Defence commission of inquiry into the fatal accident has revealed wild oscillations have occurred in Australian Chinook Ch-47 D medium-lift helicopters at least four times.
The evidence also indicates how the computer problem has been fixed in the subsequent F-model of the helicopter, a variant that the federal government had originally promised to have in service by last year.
Fairfax has also learned the D-model helicopters are being flown with makeshift seats for door gunners jury-rigged from Eskys, in contrast to proper crash seats used in the later F Model.
The stability issues were revealed by a top Defence Science and Technology Organisation aeronautical engineer during his evidence to an inquiry last month into the death of Lieutenant Marcus Case in Afghanistan.
Lieutenant Case was killed in Afghanistan last year when the D model Chinook he was a passenger in began ''porpoising'', tilting and rising violently to the point where the aircraft was pointing down at a 110-degree angle causing it to crash, roll and catch on fire.
The 26-year-old who had been riding on the helicopter's rear ramp was flung out of the aircraft and left hanging attached by just a safety strap just before the crash on May 30.
Five other crew on board were injured.
Last month an inquiry into his death heard evidence from Defence Science and Technology Organisation scientist Rhys Lehmann who had examined the causes of the crash and found problems with the helicopter's analogue Advanced Flight Control System that helped the pilots' fly the aircraft.