WASHINGTON -- The recently imposed smoking ban on many commercial flights has had one distinctly unhealthy side effect -- it snuffed out the most popular method mechanics used to spot cracks in aircraft fuselages.

Up until April when the government banned lighting up on flights of two hours duration or less, mechanics could count on tell-tale build-up of nicotine around cracks as air escaped from the passenger cabin when the plane pressurized after lift-off.


The cracks, which often are not dangerous as long as they remain small and do not link up, generally were repaired when the plane went in for maintenance.

But with the smoking ban, the nicotine is gone on many types of aircraft used in shorter flights such as DC-9s and Boeing 727s and 737s, and mechanics must now rely on much closer visual inspections and in some cases electronic inspections to detect cracks.

Fuselage cracks, particularly in older craft, have become the subject of intense Federal Aviation Administration scrutiny since an Aloha Airlines 737 ripped open at 24,000 feet over Hawaii last month, killing a stewardess.

In the wake of that accident, the FAA ordered visual inspections of all Boeing 737s with more than 30,000 takeoffs and landings and electronic inspections of those with more than 50,000 takeoffs and landings.

Those inspections have revealed a number of previously undetected cracks that, if not fixed, could lead to the kind of structural failure that occurred in the Aloha accident, the agency said earlier this week.

As a result, the FAA proposed permanent rules that would require airlines to conduct routine in-depth inspections of older Boeing 737s, including use of sophisticated electronic detection devices.

Airlines could avoid conducting the expensive inspections by installing additional fasteners on fuselage joints to ensure against structural failures.

Despite the tough FAA action, some lawmakers in Congress have questioned the adequacy of detection procedures that up to recently have depended largely on nicotine stains.

Reps. Tom Lewis, R-Fla., and Dan Glickman, D-Kan., introduced legislation last week that would require the FAA to conduct extensive research into better detection equipment and systems.

'The easiest and most common way to detect leaks in the fuselage today is to look for tobacco smoke stains on the outside metal,' Lewis told his colleageus in introducing the bill. 'Not very reassuring, is it?'