A Matter of Trust

Faith in the mechanic is essential, yet accidents show that sometimes that trust is misplaced.


Pilots and even aircraft owners have a tendency to take airplanes at face value. If a friend or acquaintance asks you to go flying, do you ask to see the maintenance logs, check the applicable ADs, or even tag along on the preflight?

The fact is that the FARs put the onus on the airplane owner to maintain the aircraft in an airworthy condition, and most people trust that the rules have been followed. And when someone asks you to go flying with them, odds are you accept that persons piloting skills as a given without even asking a few simple questions.

The last flight of an Aero Commander 500-B shows just how misplaced that trust can be. The aircraft was being positioned from Lancaster, Texas, to Laredo, Texas, after having some maintenance work done. The owners usual pilot was unavailable, so the mechanic agreed to make the 334 nm flight.

The mechanic held a private license and a multiengine rating. There was no record that he had any experience in a Twin Commander other than a brief post-maintenance check flight with the owners pilot a few weeks earlier. Because he did not have an instrument rating, he asked an acquaintance to fly right seat. The second pilot had a commercial license and was a multiengine instructor. Although he had logged no previous Twin Commander time, he had more than 4,800 hours and had completed a Part 135 check ride a couple of months earlier in a Piper Seneca.

They were joined by a passenger, who owned a single-engine aircraft and had about 35 hours of dual instruction in an Aero Commander 560-A.

The pilots decided to file an IFR flight plan because ceilings were reported between 500 feet and 1,400 feet and visibility was about five miles with haze and fog in the area.

After the pilot filed his flight plan, he was given a clearance with a void time, but could not get airborne in time. He asked that the clearance be extended a few minutes and finally took off at about 4:17 p.m. As the aircraft climbed through 4,000 feet on its way to its assigned altitude of 5,000 feet, the controller cleared the plane up to 6,000. The pilot made an unexpected response.

We got a problem here, ah, were gonna drop down. We, ah, were gonna go VFR. We have an engine problem.

The controller replied that he understood that to be a cancellation of the IFR flight plan. The pilot relayed that they were losing fuel flow to the right engine, and verified to the controller that the plane was still under control.

At about that point the controller lost radar contact, and radio communications became spotty because of the planes low altitude. A nearby National Guard helicopter began relaying messages between the controller and the stricken plane.

The pilots aboard the Twin Commander troubleshot the problem and concluded there was nothing they could do to restore power. They feathered the engine and considered their options. One was to return to Lancaster, the other was to proceed to Ennis, a few miles ahead. They opted for Ennis.

Through the National Guard helicopter, the pilot reported a right base for runway 15, a 3994-feet x 50 feet paved runway. The controller asked the helicopter to shoot the instrument approach into Ennis and check on the airplane, and the chopper pilot agreed.

Several witnesses saw the airplane enter a close right base for the runway. The airplane was low and slow, with the wings rocking wildly as it closed in on the airport.

The pilot-rated passenger later recalled that everything seemed fine as they turned base to final. He had been sitting sideways in a rear-facing seat, observing the two pilots in the front addressing the problem and flying the plane. With landing seemingly assured, he turned around in his seat and tightened his seat belt for landing.

After enough time passed that I felt we should have been landing, I turned around and looked forward, he told investigators. We seemed to be over halfway down the length of the runway, but no longer lined up with it.

He added that the airspeed seemed slow and it appeared the airplane was about 40 feet off the ground. Thats when the pilot apparently decided to try to make a go-around. He raised the gear handle. The nose pitched up, and the airplane entered a Vmc roll. As the wing went down, it struck two power lines 28 feet above the ground and cartwheeled to a stop.

The left seat pilot was killed on impact. The right seat pilot, trapped in the wreckage, held on long enough for the ambulance to get there. As paramedics worked on him, however, he succumbed to his injuries. The passenger in the back was seriously injured, but walked out of the airplane under his own power and met rescuers headed for the crash site.

When investigators examined the wreckage, they noted a number of problems that led to the crash.

The failure of the right engine was traced to a fuel distributor valve in the right engine. On a test stand it would not deliver fuel to the fuel injector nozzles. The diaphragm inside had deteriorated to the point where it ruptured and the filter was clogged with debris. When a good part was installed, the fuel injector assembly worked properly.

All of the bottom spark plugs in the left engine were found to be lead-fouled, as was one of the upper plugs. Three of the fouled plugs were connected to one magneto, and four were connected to the other. A magneto check would have shown about the same drop on each side, but the engine would have been incapable of producing full power. When the mags were tested after the crash, only five of the spark plugs produced spark, each in a different cylinder. A review of the records from when the engines were overhauled does not include any reference to which ADs and service bulletins were complied with, and there is no record that the magnetos and fuel system components had ever been overhauled.

In addition, the airplane was found to be 116 pounds overweight at the time of the accident, with the center of gravity 1.3 inches in front of the forward limit.

In retrospect, the airplanes fate was sealed long before the pilot ever started the engines.

The airplane was imported from Canada in 1992 by an aircraft dealer. The engines were overhauled and a few months later the plane was purchased by a company that planned to use it as a backup plane for the buyers Federal Express delivery service contract. A year later, the company lost the FedEx contract and the airplane was put into storage. Two and a half years later, the buyer contacted the aircraft dealer and sold the airplane back to him in mid-1996.

Among the inquiries the dealer had on the Aero Commander was one from a potential buyer that was interested enough to conduct a prepurchase inspection in March 1997. The squawk sheet was long, with 59 items. Some of the items were minor, but many had direct impact on the airworthiness of the airplane, including fluctuations in fuel flow and pressure. The potential buyer declined to complete the deal.

In April, the final owner reviewed the month-old prebuy and opted to purchase the airplane. Over the next several months, maintenance proved to be problematic. The airplane had an annual inspection in August, but only a few weeks later was returned to the shop with a number of discrepancies, including low fuel flow and leaky tanks. At one point, the right engine wouldnt operate without the boost pump on.

Additional work was done on the fuel system, and debris was found in the fuel filters and fuel lines. The mechanic and pilot concluded the debris was paint blast media that encroached when the airplane was painted. Had they checked, they would have found that the airplane had been chemically stripped and not blasted.

In September, the airplane was flown to Lancaster for maintenance on the exhaust system, and on that flight additional leaks were detected in the fuel tanks. The aircraft was grounded for three months as mechanics fixed the exhaust leaks, replaced the tanks and sent both sets of fuel injector servos and nozzles out for repair.

The owners pilot returned for the airplane in December. When he conducted a runup on the right engine, he noted that the magneto drop was barely within limits. He flew a short test hop and found no other discrepancies. When he landed and topped off the tanks, however, the new cell failed.

The mechanic agreed to retime the magneto and repair the fuel leak. By then, however, the owners pilot was unavailable and the owner arranged for the mechanic to fly the airplane to Laredo.

The passenger noted after the accident that the two pilots conducted a careful preflight. He said he paid close attention because he knew the airplanes troubled history.

Despite the airplanes history of fuel flow problems, none of the various mechanics who had overhauled the engines, performed annual inspections and were asked to troubleshoot the fuel fluctuations looked at the fuel distributor valve. If they had, they would have noticed that the units were subject to a 1980 service bulletin requiring the synthetic rubber diaphragm to be replaced with a silicone one, although the bulletin allowed current stock to be used and did not require the replacement by any specific date. A check of the logbooks would have shown that the replacement was not made.

Every pilot has implicit trust in the mechanics who work on the airplane he or she is about to fly, or else the plane would never leave the ground. As this flight shows, however, a little bit of skepticism is essential to catch omissions mechanics may make from time to time, as well as to detect those procedures that dont fit with a responsible attitude toward maintenance.

-by Ken Ibold


Please enter your comment!
Please enter your name here