Capital providers in the aviation insurance market have been accused of having lost their appetite for risk.
Leading aviation broker Jonathan Palmer-Brown, chairman of Aon's specialty division, said capital backers appeared to be shying away from the big profits associated with big risks.
A number of insurers have publicly expressed reservations about writing major airline risks.
Brit pulled out of the sector entirely, while helicopter specialist Hardy's chief executive Barbara Merry said recently the company "would not be participating too excessively" in the market.
Palmer-Brown cast doubt on insurers' arguments that lack of aviation reinsurance made them want to exit the sector.
He said: "If you look back, there's never been any shortage of reinsurance."
Global premium had to total something above $2bn for underwriters to make a profit, but the precise figure depended on the eventual size of the WTC loss and its allocation within the market.
"That's the difficult and vexing question," he said.
"Have capital providers totally lost their appetite for risk? Yes, there is an element of that."