“This is 176, we’re coming in over Cape Cod descending, we have a magnetic chip detector light, we’d like to declare an emergency — and we’re heading for home plate.”
It was August 1978. One seventy-six was a Grumman US-2B Tracker, a Navy utility plane nicknamed “Stoof” from the type designation of one common model, the S-2F. A high-wing twin with two radial engines of 1,525 hp each, Stoofs were anachronisms in a Navy that had gone nearly all-turbine. Superseded in their original role of carrier-based anti-submarine patrol, they found work ashore in personnel and materiel transport and pilot proficiency. “Home plate” for this one was NAS South Weymouth, just across Massachusetts Bay from Cape Cod. The purpose of the outing was to re-qualify a pilot who had more than 3,500 hours in the type but had been away from it for five years.
Eleven minutes later, the S-2 was approaching the shore at Plymouth. The oil temperature in the questionable port engine, which had been rising, was coming down. But now the engine began to run rough. The pilots shut it down, but the prop feathered only partially and the engine continued to windmill.
A Sea King helicopter that happened to be in the vicinity joined up on the Grumman and reported that it was trailing smoke. The helicopter gave the crew a vector to South Weymouth — they were somewhat south of a direct course — and mentioned only belatedly that the smoke was coming from the “good” starboard engine.
Nineteen minutes after declaring an emergency, 176 reported that the starboard engine was now showing a chip detector light as well — meaning there were metal fragments in the oil sump. “If we put our gear down and they won’t come down, we’re coming in anyway,” they said. “We may have to ditch it, so stand by. … OK, both engines have quit, we’re gonna have to take it in.”
“Come right,” the helicopter pilot said. “There’s a field just to your right.”
“Yeah, I got it.”
“Tower, 176 is putting it in a field, he’s 4 miles southeast … Crash! Crash! Crash! 176 and he’s burning!”
The Tracker had overshot the field, which contained baseball diamonds, and crashed into the woods beyond it. Both pilots died.
The investigating officer determined that the formal cause of the accident was the failure of both engines, which left the crew with no alternative to crash landing the airplane. The left engine’s connecting rod journals were found to be so badly worn that the valves were hitting the pistons; the right engine had swallowed an exhaust valve after the valve seat fell out.
The airplane had been carelessly maintained. Out-of-limits parameters had been ignored or dealt with inappropriately. For example, two weeks before the accident, when the magneto timing on one of the engines had been found to be 3.5 degrees too advanced, the 3.5-degree correction had been added to the spark advance rather than subtracted from it. Low oil pressure, noted a month before the accident and possibly indicative of severe wear, was one of several discrepancies that should have grounded or “downed” the aircraft, but there was a “general hesitancy” to down airplanes and “general apathy” among the personnel assigned to servicing the S-2s.
Two other issues were raised by senior officers providing “endorsements” —which usually means dissents — to the original report. One was the fact that the aircraft commander was current in the S-2 but relatively inexperienced, whereas the pilot being re-qualified, who was his senior in rank, was highly experienced but had been away for five years. These may appear to be merely technical distinctions, but they could have affected the way the crew responded to the initial emergency. Who deferred to whom? And which pilot was better qualified to make decisions?
The other issue was the crew’s decision to return to “home plate” after declaring an emergency rather than head to any of five other airports, civil or military, that were closer by. By the letter of the operations manual for the S-2, a chip light combined with any other indication of engine trouble — in this case, rising oil temperature — required immediately shutting down the affected engine. Instead, they kept it running. One endorser noted that if the pilots had shut down the port engine while they were still over the Cape, it “would have been available for the pilots to bring back on the line when the starboard engine ultimately began to fail.” This seems optimistic, considering that the unfeathered propeller would have made it difficult to maintain altitude and would have put additional strain on the other engine, possibly hastening its demise.
The question of how to proceed after an engine failure in a multiengine airplane that can continue to cruise on its remaining engine or engines can be a tricky one. Land at the earliest opportunity? Land at the nearest maintenance base that can handle major engine repairs? Continue to a convenient airline hub or to one’s own home field or destination? Theoretically, at least, a twin with one prop feathered is just a lopsided single-engine plane, and no one feels obliged to land at the first opportunity just because an airplane has only one engine.
A hypothetical explanation for the conduct of the crew is that the older pilot had experienced other engine problems during his 3,500 hours of S-2 flying, believed that the plane would return to its nearby base without difficulty, and had no reason to suspect that a second engine failure would occur — under normal conditions, a fantastically unlikely event.
One endorser noted that in the nine months since the accident the quality of S-2 maintenance at the base had been improved, and that, in any case, the S-2 — a “relatively complex aircraft” compared with a turbine — would soon be replaced by more modern equipment. “Under the conditions of austere manning found at Naval Reserve air stations,” he wrote, “it is not surprising that this old aircraft did not receive the detailed attention needed to maintain a thoroughly safe program.”
The third and final endorser criticized this last observation in rather scathing terms, finding “alarming … its apparent implication that various degrees of safety (safe as opposed to thoroughly safe) exist within naval aviation.”
And yet, that was certainly the case. It’s the case throughout aviation. Military aviation is particularly well supplied with rules and procedures and expects that everything will be done “by the book,” but it’s obvious that in real life a certain amount of judgment and improvisation will always exist. Maintenance of airplanes, as of automobiles, is not a cut-and-dry affair. Mechanics make daily judgments about wear, expected useful life, and cost of replacement. An engine that has run to its TBO is not the same engine as when it was new. Is it as safe now as it was then? Safer, perhaps, because its period of infant mortality is well behind it? Is this tire worn out, or does it still have a few dozen landings left in it? Should oil be changed at 50-hour intervals or 25? Is this compression test definitive or an odd outlier?
Maintenance judgments play a particularly important role in the world of amateur-built airplanes, which now constitute a large and growing portion of the general aviation fleet. Each builder is the FAA-anointed repairman of his own airplane. The conflict of interest is obvious. As the person who has to pay the bills, the amateur builder-mechanic has an interest in deferring maintenance, and some are certain to feel, at some point, that “safe” is good enough and “thoroughly safe” is a luxury they cannot afford.
Notwithstanding the indignation of idealists, safety in aviation comes in infinite shades of gray. We rely on both pilots and maintainers to discriminate wisely among them.
