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Mark Lacagnina |
This article first appeared in the May 1996 issue of AVIATION SAFETY and appears here by permission of Belvoir Publications.
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Gone are the days when pilots were expected to know every nut and bolt in
their aircraft. These days, pilots aren't expected to retain minute mechanical
details, but there is still much we need to know about our aircraft to stay
safe_including enough systems knowledge to understand what the various cockpit
annunciator lights and buzzers mean, and how to check them against other
indicators whenever possible.
Without this knowledge, an assumption can lead to misguided action that turns
a minor abnormality or a false warning into a full-blown emergency that seriously
jeopardizes a flight. The following accident is a case in point:
Early in the evening on Dec. 13, 1994, an American Eagle Jetstream
Super 31 was vectored for the ILS approach to Runway 5L at Raleigh-Durham,
N.C. The airport had a 500-foot ceiling and two-miles' visibility in light
rain and fog_well above the minimums for the instrument approach. After the
twin-turboprop crossed the final approach fix (BARRT), the captain advanced
the propeller speed controls, while the power controls were still in flight
idle, and told the copilot to extend the flaps to 20 degrees and lower the
landing gear. He then noticed a light flash below the engine instrument cluster.
"Why's that ignition light on?" he asked. "We just had a flameout?"
"I'm not sure what's going on with it," the copilot replied.
"We had a flameout." It wasn't a question this time, but a statement.
"What do you want me to do?" the copilot asked. "You going to continue [the
approach]?"
"Okay, yeah. I'm going to continue," the captain said. "Just back me up."
The airplane began drifting to the left while maintaining altitude at about
1,800 feet. Only a few seconds after announcing that he would continue the
approach, the captain decided to abandon it and told the copilot to "set
max power" for a missed approach.
The turn rate increased to about five degrees per second. Airspeed was decaying
rapidly, and the stall warning sounded intermittently. The copilot repeatedly
advised the captain to lower the nose. "You got it?" he asked.
"Yeah," the captain replied. But the turn continued, airspeed kept dropping,
and the airplane remained level.
The last statement recorded by the CVR was the copilot saying, "It's the
wrong foot, wrong engine." The airplane then apparently stalled and began
to descend at a rate that quickly reached more than 10,000 fpm. It crashed
through a stand of trees on a heading of 290 degrees. Both pilots and 13
passengers were killed; five passengers were seriously injured.
Series of Errors
During its investigation, NTSB uncovered a series of errors that began with
the captain's interpretation of the ignition light, which he noticed shortly
after advancing the propeller speed controls. The board believes that he
moved the prop controls rapidly, which caused a transient negative torque
condition in the left engine. For a very brief period, the prop blades were
being turned by the air loads on them, rather than by the engine. This more
typically would happen, for a longer period, if the engine lost power (i.e.,
flamed out).
The airplane's negative torque sensing (NTS) system detected the transient
condition and automatically fired the engine's igniters. If the engine had
flamed out, the sparks produced by the igniters could have restored power.
But the evidence shows that the engine had not flamed out. Therefore, the
igniters would have had no effect on the engine; but the cockpit annunciator
light ("IGN") would have stayed on for the 20-30 seconds the igniters were
fired by the NTS in response to the transient negative torque condition.
No Verification
NTSB believes that the pilot assumed he had an engine failure because the
ignition light had always been associated with a flameout during training
in the simulator. However, he apparently did not attempt to verify his assumption
by checking the engine gauges.
Propeller rpm probably was at or near 100 percent when the ignition light
came on. Anything above 90 percent on this gauge is a positive indication
the engine is running, according to the airplane's manufacturer. Verification
of a flameout also could have been achieved by advancing the power lever
and checking whether or not the torque indication responded normally.
Furthermore, the captain did not discuss his reasoning with the copilot,
and the copilot did not question the assumption. And though they tacitly
agreed on a flameout, they did not follow through by feathering the propeller,
securing the "dead" engine or cleaning up the airplane.
Investigators concluded that the CVR's recording of intermittent activation
of the stall-warning system and radar data showing that the airplane's descent
was arrested at about 1,800 feet indicate that the captain was holding
substantial back pressure on the yoke_and continued to do so despite repeated
advice from the copilot to lower the nose.
NTSB characterized as "puzzling" the captain's decision to conduct a missed
approach. Though it had begun drifting to the left, the airplane was still
well within the limits of the localizer course width and only slightly above
the glide slope. If the crew had followed through with appropriate single-engine
procedures, it would have been easier_and safer_to continue the ILS approach
and land than to try to go around.
'Wrong Foot, Wrong Engine'
Although continuing the approach would have been the safer choice, the airplane
could have gone around on one engine if it was handled properly. However,
after calling for the missed approach, the captain told the copilot only
to "set max power." He did not call for the checklist.
The copilot did as he was instructed, but he advanced only the right engine
power lever. "If he had advanced both power levers, both engines would have
responded and the perceived emergency would have been resolved," NTSB said.
Despite losing this last opportunity to discover that the left engine was,
indeed, running, setting max power on the right engine was the proper first
step for a single-engine go-around. Unfortunately, no other steps were taken.
With the flaps and landing gear extended, the Jetstream couldn't climb.
"It is impossible to determine what control inputs were being made by either
crew member, but they had little or no lateral or directional control of
the aircraft for the next 13 seconds," NTSB said. In an asymmetric thrust
condition, rudder is needed to counter yaw induced by "good" engine thrust
and "dead" engine drag. Multiengine students are taught "dead foot, dead
engine" to identify which engine has lost power; the rudder being applied
to counter the adverse yaw is on the same side as the "good" engine. Shortly
before the airplane stalled and entered a steep descent, the copilot said,
"Wrong foot, wrong engine." Did he notice that the captain was applying left
rudder, rather than right rudder, to counter the adverse yaw? Possibly, but
there's no proof of this.
Probable Cause
NTSB ascribed the accident to the captain's "improper assumption that an
engine had failed" and his "subsequent failure to follow approved procedures
for engine failure, single-engine approach and go-around, and stall recovery."
The board also blamed the airline for failing to detect and correct "deficiencies
in pilot performance and training." Investigators found that the 29-year-old,
3,500-hour captain had a checkered history. Records show that he had problems
with simulated engine failures and ILS approaches during his initial training
with Comair in 1990. After a year of flying as a probationary copilot on
Saab 340s, he was given poor marks by line captains. One believed he had
below-average piloting skills, often got "behind the airplane" and might
"freeze up or get tunnel vision in an emergency situation." Another captain
recommended that he be dismissed. But, instead of firing him, Comair allowed
him to resign.
By that time, he already had accepted an offer to fly for Flagship Airlines,
one of four regionals operated by American Eagle. No background check was
conducted_not that it would have mattered, because Comair told NTSB that
it would only have listed the pilot's dates of employment and aircraft operated.
The pilot flew right seat in Jetstreams until early in 1992, when he was
considered for upgrade to captain on Shorts 360s. Although he was written
up for unsatisfactory performance on engine failures, single-engine procedures
and crosswind takeoffs and landings, he was given additional training and
eventually passed his type rating and line checks. His performance as a captain
apparently earned him a less-than-sterling reputation among other pilots
at American Eagle. A month before the accident, he talked with his base manager
about the situation. "The base manager offered to assist him in securing
training time in the simulator, but the captain declined the offer," NTSB
said.
Lessons
The accident illustrates the potential consequences of not using available
resources in an abnormal or emergency situation. The captain did not verify
his assumption that an engine had flamed out, and he chose not to get any
help from his copilot, a 25-year-old, 3,450-hour ATP considered by colleagues
and check airmen as an above-average pilot.
It's important to keep in mind that only one minute elapsed from the time
the captain announced that an engine had flamed out until the airplane struck
the ground. This shows how quickly a situation can deteriorate when procedures
are not followed and control is not maintained.
Among NTSB's recommendations following the crash is that airlines be required
to maintain and share standardized pilot training and performance records.
This has created a furor among airlines and commercial pilots who believe
it would be an invasion of privacy. Many airlines depend on evaluation during
initial training to weed out substandard pilots. But the record shows that
it doesn't work that way; this was the fourth accident since 1987 that prompted
the safety board to recommend requirements for background checks.
Beyond biennial flight reviews, those of us who don't fly for hire are our
own evaluators. We owe it to our passengers to do a thorough, objective job
in determining whether we truly are up to snuff.
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