Aviation Safety Letter 4/2004

Beware of the Conditioned Response

by Garth Wallace

A customer rented a Piper Cherokee 140 at the school where I taught flying, and taxied it under the wing of a McDonnell Douglas DC-9. It didn't fit. The trailing edge of the DC-9's aileron neatly sliced through the top of the 140's rudder. The pilot must have felt a jerk, accompanied by the sound of ripping fibreglass, but he didn't stop. He continued to the runway, took off, flew back to our base and parked the Cherokee on the flight school ramp. He paid for the flight without mentioning the damage.

A flight instructor and student had the next booking on the aircraft. The instructor rubbed his eyes and looked again when he saw the top of the rudder. Wires for the missing rotating beacon and rear navigation light hung over the jagged edge.

Beware of the Conditioned Response

His student completed the pre-flight inspection and said, "All set?"

The instructor glared at him. "Didn't you find anything wrong with the airplane?"

"No, it looks fine. Are we ready to go?"


Several things happened over the next hour. The damage was reported to the flight school's chief mechanic. The receptionist juggled the bookings so that the instructor could have another aircraft. The rest of that lesson was spent on an intense walkaround lecture.

Later, the instructor led the discussion at the staff coffee break.

"I couldn't believe that my student inspected the airplane without seeing the wrecked rudder." He groaned and shook his head.

"It doesn't surprise me," our chief flight instructor (CFI) replied. "I bet most students would miss it. They become conditioned. We show them what to inspect, but everything looks good. When they find something, like a low oil level, we tell them it's OK for another hour. Then the pre-flight decision making is back to the instructor."

"I'll take you up on your bet," I offered. "Leave the Cherokee on the ramp and I'll send my next student to inspect it. I bet he snags the damage."

"Who's the student?" the CFI asked.


Melville Passmore was my highest time student. He was a farm-smart country boy who was struggling with the academics of learning to fly, but was quick to grasp the practical. He was the most likely student to spot the damage.

Melville and I walked across the ramp to the waiting Cherokee. The CFI watched from inside. The little farmer always took the pre-flight seriously. He inspected the airplane from top to bottom, bustling in, around and under, checking everything thoroughly. At the rudder, he looked up, stopped and stared. He glanced toward me. I pretended to be interested in something else. He stood there contemplating the dangling wires for another moment and then continued inspecting the airplane. When he was done, he looked at the tail again, turned to me and said, "Ready to go?"

I couldn't believe it. My most experienced student wanted to climb into a broken airplane and fly. I had lost the bet, but I wanted to test him further. "Are you ready to go?" I asked.

"Ready when you are," he replied promptly.

"What about the top of the rudder?"

Melville looked at it and said, "It's gone."

"No kidding. Didn't I teach you to check for damage on a walkaround?" I barked.

Melville stuffed his hands into his coverall pockets and hung his head. He looked at the ground and said nothing.

"Didn't I?" I demanded.

"Yes," he replied weakly. He didn't look up.

I was about to continue my inquisition when the CFI came out of the office.

"I can guess what's going on," he called out as he crossed the short distance to the airplane.

"Tell me, Melville, did you notice the damage on the tail during your inspection?"

Melville replied quietly, "Yes."

"Why didn't you mention it?"

"I don't know," he answered meekly.

"Have you mentioned snags on walkarounds before?"

Melville lifted his head slightly. He looked at me and then at the CFI. "Yes."

"What happened when you did?"

I could tell that he didn't want to answer. He watched his feet and didn't respond.

"This is not a test, Melville," the CFI said, "and nobody is going to yell at you."

"When I asked about a balding tire," Melville replied slowly, "I was told that it would last until the next inspection. I mentioned a crack in the windshield once and was told, 'it's too small to worry about.' One time the fire extinguisher pressure was a bit low. 'It will still work.' was the reply."

I could hear myself saying these things to Melville. The CFI's point was sinking in. I had conditioned Melville to ignore discrepancies.

"Would you fly this airplane solo today?" the CFI asked.

"No," Melville answered quickly.

"Would you fly it with an instructor?"

Melville shuffled his feet a little. "If he said it was okay."

"Well, it's not okay, Melville," he replied. "This other Cherokee is available. You guys can use it for your flight today." He turned and started to walk away.

"The wing is bent on that one," Melville announced softly.

The CFI stopped in his tracks and turned around. "What did you say?"

Melville stared at the ground and mumbled, "The left wing is bent up more than the right one."

The CFI walked over to the next airplane and looked at it from the front. Melville and I followed. The Cherokee was definitely sitting at a slight angle.

"I think the one oleo is lower than the other, Melville," the CFI said.

The little round farmer walked up to the airplane, squatted on his haunches and pointed at the wing root underneath. "You can see where the skin has been pulled," he said.

The CFI crouched beside him and looked. "I don't see anything," he said.

"You have to look closely."

The CFI crawled under the wing and looked up. There were stretch lines in the wing panel under the main spar and little smiles of metal skin buckled against some of the rivet heads. The airplane must have been landed hard on that side.

"How long has it been like that?" the CFI asked.

"A couple of weeks," Melville answered.

"That explains why it spins differently left and right," I offered.

"I'll get the Chief out here," the CFI said. "You two find something else to do. We're out of airplanes." He headed toward the maintenance shop. The Chief was the school's head aircraft maintenance engineer (AME).

"Have you found anything wrong with other aircraft?" I asked Melville.

"Yes," he replied shyly.

"Like what?"

"The scissors on the right gear leg of Alpha Bravo Charlie are cracked." He looked at me to see if he should keep going.


"The tail skid on Delta Echo Foxtrot has been banged into the fuselage."

I nodded for more.

"The aileron chains on Golf Hotel India's control wheels are worn."

"How do you know?"

"I turned both control wheels in opposite directions from the pilot's seat, they moved about 20 degrees."

"Well, there is only one other Cherokee in the fleet."

"Its propeller is out of track."

"How did you find that out?"

"I could feel it vibrate the last time I flew it. When I was back on the ground, I checked the track against the engine nose bowl. It's out a few millimetres."

The Chief and the CFI appeared from the hangar. The mechanic crawled under the wing. "Yup, she's been pulled all right." He jumped to his feet. "Thanks, Melville. You're pretty sharp to spot that."

The young farmer beamed at the compliment.

"With these two damaged Cherokees, my shop is going to be busy for weeks," the Chief declared. He turned to the CFI, "Both these airplanes are grounded. You guys will have to make do with the rest of the fleet."

"You don't know the half of it," I replied.

Garth Wallace is an aviator, public speaker and freelance writer who lives near Ottawa, Ontario. He has written eight aviation books published by Happy Landings (www.happylandings.com/). He can be contacted via e-mail: garth@happylandings.com.

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