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Probable Cause #58: Known Deficiencies

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This article originally appeared in Aviation Safety, Apr. 2006.

Probable Cause

It's rare to find even a brand-new airplane without at least one "squawk" -- a mechanical deficiency. Of course, the FAA would say that all equipment and components of an aircraft must be working properly or placarded as inoperative, else the airplane isn't legally airworthy. The FAA will also say that all equipment listed in the aircraft's Type Certificate Data Sheet must be installed and operating for airworthiness, and any additional equipment required by regulation for the specific operation must be in good working order. In the real world, however, it doesn't work that way, and pilots routinely launch a flight with some equipment known to be intermittent, at best. While operating with known deficiencies in equipment is rarely a good idea, there are ways to minimize the risks posed. The severity of a deferred squawk can prevent some kinds of operations, while making others more risky than they need to be. An example of the former might be a failed navigation light, making night flight illegal. An example of the latter could be an inoperative alternator, which could make just about any flight out of visual range from a non-towered home base a bad idea. I have, on occasion, flown aircraft with known squawks. It wasn't the smartest thing I've ever done, but I was careful to ensure there were no other issues with the aircraft, especially the kind that could have complicated the original problem. But I try to draw the line at engine deficiencies, especially with a single. On the few occasions I have had a known engine problem, the only flying I did was either directly over an airport in an attempt to diagnose the problem or the flight to the engine shop. But that's with a single. If I had a twin with a known problem in one of its engines, I don't know if I would be more or less inclined to fly the airplane, either normally or at all. This month's example teaches us that known engine problems are a good reason to ground the airplane until the problem can be found and fixed.

Background

Piper PA-30 Twin Comanche

On April 4, 2004, at about 1606 Eastern Time, a Piper PA-30 crashed onto airport property shortly after takeoff from the Fernandina Beach Municipal Airport, Fernandina Beach, Fla. The airplane was substantially damaged and the Commercial pilot and single passenger were fatally injured. Weather for the planned IFR flight to the Burlington-Alamance Regional Airport in Burlington, N.C., was good VFR. The airplane departed Runway 26 and its landing gear retracted. After climbing to approximately 200 feet AGL, the airplane banked to the left, quickly banked back to the right, and then appeared to stabilize. When next seen, the airplane was in a 25-30 degree left-wing-low and nose-low attitude, which continued until impact. One witness reported a sputtering sound, which he described as being similar to when power is reduced. The airplane was equipped with a JPI Instruments EDM 760 engine monitor programmed to record the exhaust-gas temperature (EGT) and cylinder-head temperature (CHT) readings from both engines every six seconds.

Investigation

Engine Monitor

A review of the pilot's computerized flight log revealed two entries describing discrepancies relating to the fuel injector systems of both engines. The first entry said, "clogged L3 injector." The second entry read, "L4 & R4 injector clogs." Maintenance personnel who performed the last annual inspection on the airplane before the accident reported finding water and corrosion in the fuel strainers, as well as water in the fuel. At that inspection, a squawk list presented by the owners included, "Check complete fuel system due to chronic injector clogging (both engines). This problem only manifests itself if the plane sits for a month or more. If flown regularly it doesn't happen." Bench testing of the left fuel servo revealed erratic fuel flow. On disassembly, contamination of the fuel diaphragm and corrosion on the center body was noted, as were debris in the fuel-control housing area and drops of water. Bench testing of the left fuel injector nozzles revealed all exhibited a poor spray pattern. The right fuel servo revealed corrosion on the fuel inlet screen and debris flowed from the unit during the start of bench testing. Disassembly of the right fuel servo revealed contamination at the regulator, and debris and contamination on the fuel side of the diaphragm. Corrosion was noted in the fuel control area, and on the fuel-control idle valve. Bench testing of the right fuel injector nozzles revealed that all exhibited a poor spray pattern. The engine monitor's stored data revealed 10 events of varying duration, including the accident flight. A total of 78 readings taken every 6 seconds were recorded during the accident flight. A review of the accident flight data revealed that at 20:22:00, the EGT reading of each cylinder of the left engine were, 1429, 1398, 1311 and 1396 degrees F, respectively. The EGT readings for the right engine were 1399, 1413, 1364 and 1384 degrees F. Readings taken six seconds later, or at 20:22:06, indicates the EGT reading for all cylinders of the left engine were 710, 710, 726 and 753 degrees F., respectively. At the same time, the readings for all cylinders of the right engine were 1392, 1418, 1364 and 1384 degrees F, respectively. Subsequent data -- up to the point at which recording stopped -- all included sharply reduced EGT readings from the left engine.

Probable Cause

The National Transportation Safety Board (NTSB) determined the probable cause(s) of this accident to include, "The failure of the pilot to feather the left propeller and his failure to maintain control of the airplane following a loss of engine power from the left engine resulting in the in-flight collision with terrain. A factor in the accident was the loss of power from the left engine for undetermined reasons." It's easy and obvious to point to chronic water and debris contamination as the source of the airplane's injector clogs. What's not so obvious is why the operators didn't demand that the fuel system be more closely inspected. As we have preached in the past, installing and learning to use an engine monitor, especially one that stores data, can be invaluable when diagnosing operational problems. It's a shame that a definitive examination of this data didn't occur until after the airplane had crashed.
More accident analyses are available in AVweb's Probable Cause Index. And for monthly articles about safety, including accident reports like this one, subscribe to AVweb's sister publication, Aviation Safety.

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