Misunderstanding: What We Have Is a Failure to Communicate

A witness saw it in a turning dive, trailing smoke. There had been no distress call from the airplane, no indication that anything was wrong.

That the engine, retrieved from 3 feet of mud, had been turning at impact was indicated by the chordwise scratches on the propeller blades. Inspection of the engine revealed only one anomaly: The magneto hold-down nuts, which are normally torqued to a specified value in order to clamp the magneto flanges tightly against the crankcase, were no more than finger tight.

National Transportation Safety Board (NTSB) investigators dug into events preceding the accident, and a curious story developed.

Six days earlier, the 100-hour pilot, 53, had taken the airplane to his mechanic because of an excessive mag drop. The mechanic checked the spark plugs, replaced a couple of bad ones, but did not test run the engine.

Three days later the pilot returned while the mechanic was working on another plane. He got into the 140 and started the engine. The mechanic, and a couple of bystanders, could tell it was still not running properly, and the mechanic signaled the pilot to shut it down. The pilot commented that he thought the engine seemed better, but the mechanic told him that the plug swap had obviously not corrected the problem and that he would do further work on the airplane later, most likely the following week.

That conversation took place on a Wednesday. The mechanic worked on the other plane for the next two days, and on Friday, knowing that bad weather was expected on Sunday, he moved the 140 back into the owner’s hangar.

In the meantime, the pilot of the 140 had planned to fly with his wife and a friend to a nearby airport for lunch on Saturday. His wife had to cancel, however, because her father was ill.

Some details remain unclear. The pilot must have misunderstood the mechanic and believed he had merely said that he would work on the plane “later,” meaning, perhaps, later that day or at some time in the next two days. We don’t know whether the pilot already knew on Saturday morning that the plane was in his hangar or found it there and assumed that the remedial work had been completed.

We do know, however, that the pilot did not communicate with the mechanic between Wednesday and Saturday, although they were personal friends and had each other’s contact information in their phones.

We inhabit a world of assumptions. In the pilot’s mental picture of the world, the plane was fixed. In the mechanic’s, it wasn’t. Unfortunately—or maybe not—mental worlds are invisible to one another.

Since the pilot went to the airport on Saturday intending to fly, it’s apparent that it was not the fact that he found the airplane in his hangar that persuaded him that whatever had been wrong had been corrected. He already thought so, and the fact that the plane was in his hangar merely fit in with his preconception. Presumably the pilot performed a run-up and found the result acceptable, just as he had on Wednesday when it was not he, but listeners outside the airplane, who could tell that something was still wrong with the engine.

Never doubting that the plane was safe, the two men embarked on their lunch flight. The Cherokee flew northward for about 35 miles at 1,700 feet agl before it began to descend at 500 fpm. The rate of descent diminished at first, then abruptly increased to 1,500 fpm. Analysis of the flight path suggested that the airplane stalled out of a steeply banked turn.

Since the loose magneto hold-down nuts were the only irregularity investigators found in the engine, the NTSB concluded that the magnetos had probably rotated in flight, changing the spark timing and reducing the engine’s power output. Evidently the power loss, possibly accompanied by rough running, alarmed the novice pilot, who had acquired his private license just five weeks earlier. The unpopulated level terrain below offered many options for a safe forced landing, but the NTSB’s finding that the airplane had probably stalled out of a steeply banked turn hints that the pilot was not planning a forced landing when he exceeded the critical angle of attack, but rather was turning around in order to head back home. 

The determination of the “probable cause” of an airplane accident is complex and somewhat arbitrary.

Rarely is the answer a single unforeseeable event, such as a bird strike or a broken crankshaft. Far more often, accidents arise from chains of causes that may extend backward to a point in time long before the fatal flight began. Along with the main probable cause, subsidiary causes can be included as “contributing.” The NTSB’s task, therefore, is to arrange causes in a hierarchy, with the most consequential at the top. 

In this case, the causes of the accident were several.

First, there was the maintenance activity, of unknown date, that left the magneto hold-down nuts loose in the first place. The NTSB did not attempt to determine when or how that happened. Next, there was the misunderstanding about when the mechanic would get back to working on the Cherokee. Finally, there was the failure of airmanship on the part of the pilot. Faced with a partial loss of engine power, he did not, first and foremost, maintain a safe airspeed.

Each link offers a chance to break the causal chain.

The airplane should not have been in service with loose magneto nuts—but that horse had left the barn long ago. The pilot should not have flown the airplane without obtaining the mechanic’s verbal or written assurance that the problem with the engine had been found and corrected. When the engine began to run rough, the pilot should have trimmed to glide speed, kept a light hand on the yoke, and chosen which of a wide selection of open fields and country roads to alight on.

The NTSB chose to place at the top of the causal hierarchy the pilot’s failure to verify that the airplane had been released from maintenance. In an odd subordinate clause, this “resulted” in a partial loss of engine power—a phrasing that minimizes the importance of those loose nuts which, in another interpretation of events, could be seen as the primary reason for the accident. The pilot’s “failure to maintain adequate airspeed” is demoted to a merely contributory role.

According to a document in the accident docket, the mechanic “now uses pink ‘do not fly’ stickers on airplanes he is working on, but has not yet returned to service.”

Note: This article is based on the National Transportation Safety Board’s report of the accident and is intended to bring the issues raised to our readers’ attention. It is not intended to judge or reach any definitive conclusions about the ability or capacity of any person, living or dead, or any aircraft or accessory. 

This column first appeared in the November Issue 952 of the FLYING print edition.