After tear in a 737, what's old for a plane

How old is too old for a passenger airplane?

Most travelers don't think twice about it - although there's something unsettling about easing into your seat and finding the armrest still has an ashtray built in.

But fliers may be more worried than usual after a 1.5m hole opened in the roof of a 15-year-old Southwest jet earlier this month. Southwest quickly grounded 79 of its older Boeing 737s for inspections.

A well-maintained plane can fly for decades. Older planes do need more repairs, but experts say an aircraft's age has never been the cause of a passenger death. Pilot training and fatigue, as well as frequency of aircraft maintenance, are larger safety issues.

The average age of jets flown by US airlines is 11 years, slightly above the world average of 10 but far shy of the 28 for Venezuela's fleet - the oldest of any country with more than a handful of jets.

Theoretically, a jet could continue flying indefinitely as long as an airline maintained it, says Bill Voss, president and CEO of the Flight Safety Foundation.