The nation's system for keeping planes flying safely in wintry weather is fundamentally flawed because pilots cannot determine at takeoff whether their planes are free of nearly invisible but potentially lethal ice, pilots and safety officials say.
The system for preventing airline accidents as a result of icing has come under intense scrutiny following the crash Sunday of a USAir jet at New York's LaGuardia Airport. Icing of the wings is a prime suspect in the crash, which killed 27 people.
Even traces of ice on the leading edge of a wing can cause disaster bydramatically reducing the lift that keeps a plane aloft. Under Federal Aviation Administration regulations, it is the responsibility of the pilot to assure before takeoff that the airplane is clear of ice and snow. Critics of the FAA regulations say that responsibility is impossible to fulfill because ice cannot always be detected by flight crews making observations from the cockpit or cabin windows.
According to airline pilot Dennis Petretti, New York chairman of the Allied Pilots Association, it is impossible to say with certainty if it is safe to take off.
"If you're sitting in the cockpit you don't have the data," he said. "In the end you're just not sure. There can be a thin layer of ice."
"You tell me how you can see clear ice on the wing," he said. And even if a pilot can see the wing, he can't see other crucial areas from the cockpit. "I can't see the tail surface. Who the hell knows what's on the fuselage."
Pilots are not the only ones critical of the current rule. Safety experts agree that the responsibilities assigned to the pilots are impossible to fulfill under current procedures.
John P. Galipault, president of the non-profit Aviation Safety Institute, said it is unfair that pilots be forced to make life and death decisions based on inadequate information. "Everyone is putting the gun to the pilot's head," he said. "You just can't let him be in a situation of too many unknowns."
Pilots waiting in line to take off have to weigh whether the de-icing fluids have continued to keep the plane clear of ice. At that point, the best a pilot can do is look out the cockpit window or walk back to the passenger compartment for a closer look at the wings. "Do we want him to go back in the cabin, lean over somebody's grandmother and look out a scratched up oily window in the dark and expect him to see any ice, which may be transparent?" Mr. Galipault asked.
He doesn't think these kinds of visual inspections are adequate. The rule putting responsibility on the pilot to determine the presence of ice is unworkable, he said.
The FAA defends its standard.
Paul Steucke, the manager of the FAA's news division, said the agency remained convinced that pilots inside their planes can determine with absolute certainty whether snow or ice is on their aircraft.
"Yes you can. Pilots do it all the time. They determine on a regular basis that the aircraft they are in requires de-icing."
It is, however, a tricky business at best. For example, Fokker 28s, the kind of plane that crashed at LaGuardia, come equipped with a black stripe that wraps over the leading edge of each wing, the most critical area for ice build-up. That stripe is designed to appear duller if ice forms over it, offering an additional visual cue to assist the pilot in spotting ice. These planes are also equipped with lights that shine on the wings and the stripe to make spotting ice easier.
But even those special aids may not have been enough to help the USAir crew that crashed at LaGuardia. According to the co-pilot, he and the captain repeatedly checked the wing before deciding to head down the runway.
"The co-pilot said he checked for ice on the wings at least three times, perhaps as many as 10, and he noticed the captain checking as well," said Ted Lopatkiewicz, spokesman for the National Transportation Safety Board, which is investigating the accident.
In fact, despite its insistence that visual inspection is adequate, the FAA in January began to require hands-on checks for ice before takeoff of DC-9-10s.
In its directive, the FAA noted that the McDonnell Douglas DC-9-10 had been involved in five accidents involving "contamination" of the wings by ice.
The FAA observed, "Although Federal Aviation Regulations . . . prohibit takeoff with ice, frost, or snow on the wings, in each reported accident, it was apparent that the ice buildup on the wings was not noticed or detected by the flight crew prior to takeoff."
The DC-9-10 is considered especially vulnerable to ice problems. Its wings do not have devices known as slats that increase a wing's lift during takeoff and landing.
The Fokker 28 also lacks wing slats. That fact has raised concern that these planes may also be particularly prone to loss of lift because of ice contamination. The FAA's Mr. Steucke said his agency had been considering applying the hands-on inspection rule to the Fokkers before the LaGuardia crash occurred.