Falling Star

Shop mistake leads Aerostar to lose a cylinder, and pilots return to the airport comes up short


Confront a pilot with a statement like, You pilots are a smug bunch and you probably wont get much argument. Truth is, ego is part of the game.

As the pages in the logbook accumulate, the feelings of been there, done that grow too. Not quickly, perhaps, but insidiously. The eye of experience heralds the look of confidence.

While experience sometimes leads to complacency, most pilots take their responsibility seriously – even enjoy it and the ongoing training and quest for proficiency that comes with the pilot certificate. Conscientiousness may be admirable, but sadly it sometimes is not enough. Mistakes do happen, and sometimes they happen at the worst possible time.

The owner of an Aerostar had delivered the airplane to a maintenance shop because the airplane was burning four quarts of oil per hour in its left engine. The airplane remained there for a week, and three mechanics worked on it between other jobs.

A compression check found the No. 1, No. 3 and No. 6 cylinders needed attention, so the mechanics decided to pull all three in order to hone the barrels and replace the rings. In order to remove the No. 6 cylinder, the engine had to be removed from the engine mounts. As long as the engine was pulled, the lead mechanic decided to remove the No. 5 cylinder as well.

With the backside of the engine exposed, the mechanics noticed that the rear oil cooler, mounted behind the No. 5 cylinder, had a broken mounting flange. It was a good catch, and the repair was made while the engine was off the mounts.

The mechanics set about repairing the cylinders and installing new rings. The No. 5 cylinder was repaired first, and slid back onto the engine. The shops standard practice was that a repaired cylinder would be slid into place and held with one nut, which would be started only. The other seven would be left off as a reminder that the cylinder needed to be torqued down. For some reason, all eight nuts were replaced and put in finger-tight.

When the No. 1 cylinder was replaced, the prop was loosened and slid forward in order to help the cylinder go on straight. A mechanic who had been out of the shop during the morning set about tightening the No. 3 and No. 6 cylinders while another mechanic reinstalled the prop and spinner. That Thursday afternoon had grown long, and the mechanics called it a day.

Wrapping It Up
When the shop opened the next morning, the mechanics got an early start on the Aerostar. They installed the rest of the nuts and mounting plates on the No. 1 cylinder. Then one mechanic noticed there were four sets of valve train lifters to be reinstalled. The mechanic reinstalling the parts, who held an A&P and an IA, decided that either the lifters from the No. 5 cylinder had been removed to check the valve train clearance or else the mechanic who disassembled the parts thought they needed to be removed to allow better access to the other cylinders. He knew the No. 5 cylinder had not been repaired.

The engine reassembly was completed and the engine was reinstalled.

Another AI inspected the work and found a couple of items that needed to be tied down and those were quickly remedied. The airplane was pushed outside and the engine was test run at low power.

The test revealed no leaks, but one of the mags on the left engine was found to have an ungrounded P lead. A broken wire was discovered and repaired. The team conducted a full-power runup and tested the operation of the engines. They checked for leaks and found everything in order. They topped the fuselage tank and parked the airplane outside.

During the afternoon, the owner of the Aerostar called the lead mechanic and asked if someone could pick him up in Philadelphia, 60 nm away, to pick up the airplane because he would like to get an early start the next morning, a Saturday. A pilot was dispatched in a Grumman Tiger, and at about 8:25 p.m. the owner of the Aerostar arrived to pick up his airplane to fly it back to his home field.

By then the airport was quiet, with one employee getting ready to go home. The pilot who picked up the owner agreed to hang around for a few minutes in case there was a problem with the airplane.

The owner conducted what the ferry pilot called a thorough preflight and started the engines. He let them warm up for a couple of minutes and then began to taxi toward runway 27.

I wanted to watch him takeoff because an Aerostar is my favorite multi-engine airplane, so I usually watch when one takes off or lands, the ferry pilot told investigators later. From where I was I could not see the end of the runway where he did his runup, but I heard it and everything sounded normal.

Up and Away
Shortly after the Aerostar began its takeoff roll, it became visible to the ferry pilot. It rotated normally and began its climb into the night sky.

Then, a few seconds after it crossed the departure end of the runway, the engine sounds decreased more than normal. The witness looked up and saw the airplane returning, passing over the field at about 400 to 500 feet agl, with the engine sounds low, but above idle. He thought maybe the owner had decided to return and was trying to get his attention so he wouldnt leave. The witness looked up as the airplane passed overhead. He saw a silhouette against the sky, but couldnt tell if the gear was up or down.

As he crossed the building he was going to the right at an angle that would widen his pattern. I still did not know for sure if he was coming back so I watched to see where he went, the witness said. I saw him turn a pretty sharp left base and I thought he could not have that much of a problem or he would not be turning that sharp that close to the ground.

The witness lost sight of the plane as it flew the base leg, but about 15 seconds after the airplane turned base he heard the engine sound increase. That was right about the time the airplane should have been turning from base to final. A bare second after the engine sound increased, the airplane hit the ground with a sound the witness described as the tailgate of a dump truck when it slams shut.

A farmer who lives next to the airport heard the airplane take off as well. Although not a pilot, he said he had grown to know the sounds of airplanes taking off.

This one did not sound right at all, he told investigators. When it took off it made a terrible sound. It was not till a minute later I heard a big blast.

The airplane wreckage was found inverted about 1,500 feet from the end of the runway and about 400 feet short of the extended centerline. The debris path showed the airplane was headed toward the runway at the time of impact. From the distribution of the wreckage, it appeared the airplane crashed inverted. The airplane owner was killed.

The left prop was feathered, and the No. 5 cylinder and piston had separated from the engine and were found along the debris path. The right engine showed damage consistent with a maximum power setting.

In its investigation, the NTSB found that some of the cylinder nuts on the left engine were not torqued sufficiently. The board could not determine whether the improper torque value was the result of improper installation or impact forces during the accident. In the five cylinders that remained, 15 of the 40 cylinder nuts were found to have low torque. Thirteen of those were in the cylinders that had been repaired.

Investigators checked the torque wrenches used at the shop, and they were found well within specifications.

The potential for mechanical trouble was evident elsewhere as well.A check of the aircrafts maintenance records, both in the aircraft logs and the maintenance shops, could find no evidence that the airplane had undergone an annual inspection for more than 3 years. An engine inspection apparently had not been conducted in 2 years.

What Went Wrong
The pilot had logged about 1,200 hours, including 400 in the Aerostar and 11 in the previous month. His last BFR had been conducted 22 months before the accident, and he had done that review in the Aerostar as well.

The NTSB determined the accident was caused by the pilot allowing the airplanes speed to drop below Vmc while on approach to land following the engine failure. The question then becomes, why did the pilot get too slow?

The airplane was lightly loaded and, because it was the Aerostar production prototype, serial number 0001, had a low empty weight anyway. Its single-engine performance should have been acceptable given the airport elevation of 458 feet msl and the temperature of 68F.

The Aerostars single-engine rate of climb is listed at 240 fpm at maximum gross weight, and the airplane was more than 1,000 pounds under gross.

In the comfort of a chair at home, its easy to link the failure of the left engine and the fact that the loss of control appeared to coincide with a left turn.

The probability that the left wing stalled with no available rudder to pick it up is hard to miss. But it also appears the pilot was in a hurry to get it on the ground – essentially ignoring the performance that leads many pilots into twins in the first place.

In the clear vision of hindsight, feathering the self-destructing engine and extending out on a gradual climb, then turning leisurely back to the airport would have made more sense.

Of course, thats easy to say when youre not listening to an engine trying to vibrate off the wing.

The trail of mistakes that led to the pilots doom may seem obvious in retrospect, but who has not urged a mechanic to finish up a job because of an impending trip?

What mechanic has not made assumptions about what others have or have not done?

How many multi-engine pilots neglect practicing engine-out procedures (at night, even) except when BFR time comes around?With experience comes the necessity to make sure your smugness is not only earned, its deserved.

-Ken Ibold


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