What you don’t know could kill you
WPR12FA001
By David Jack Kenny
The prepurchase inspection by a disinterested A&P—preferably one deeply familiar with that specific make and model—is usually the best way to assure that a prospective buyer understands what it will cost (beyond the purchase price) to make sure an aircraft is safe, reliable, and airworthy. Buyers who are themselves experienced aircraft mechanics may be able to perform their own; the rest of us are best served by engaging an independent expert who has no ties to buyer or seller and earns the same fee whether the sale goes through or not. While the rationale is usually presented in financial terms, a thorough prepurchase inspection can also be a lifesaver, particularly in the case of an aircraft that hasn’t been flying regularly.
Early in the afternoon of Oct. 4, 2011, three men met at the South Valley Regional Airport about 10 miles south of Salt Lake City. One owned a homebuilt two-seat Pulsar airplane; the second had decided to buy the Pulsar to train for his sport pilot certificate. He had brought along his CFI for the 53-nautical-mile hop south to his planned base at Nephi, Utah.
The transaction was completed quickly, but the seller had one concern. The Pulsar is a small airplane, with a 25-foot wingspan and empty weight typically in the 500-pound range. Like many, this example was powered by a 65-horsepower Rotax 582 engine. When they’d struck the deal two weeks earlier, the seller had asked about the weights of the two men who would be flying it away, and was told each was 180 to 190 pounds. However, at first glance the instructor appeared to be bigger, raising the possibility that together they might crowd the Pulsar’s 1,000-pound maximum gross weight. The seller advised them not to add any fuel to the nine gallons already on board until they had done the weight-and-balance calculations. After giving them the airplane’s weight-and-balance form, its keys, “a box full of airplane associated paperwork,” and a briefing on its systems, he returned to work.
After a stop in the run-up area, the Pulsar taxied out to depart from Runway 16. At least five witnesses watched. They agreed that it lifted off in the first half of the 5,860-foot runway but remained in ground effect, barely able to climb, and they described “a repeated porpoising sequence” in which the airplane would pitch up slightly and climb a few feet before the pilot lowered the nose to regain airspeed. As it neared the departure end, one (a CFI himself) radioed, “Experimental aircraft on departure, are you having technical difficulties?” The instructor responded, “No, it’s just a weak aircraft.”
Related links
Engine and Propeller online course
Mountain Crash Real Pilot Story
“First-Flight Fiascoes” Safety Pilot article
It took the Pulsar half a mile beyond the end of the runway to reach an altitude of about 75 feet agl. At that point, its pilot attempted a shallow right turn. Almost immediately, the airplane rolled into a bank of almost 90 degrees, the nose dropped 45 degrees, and it crashed into a soccer field, killing both men instantly. The ground scar beneath the wreckage was only three feet long.
According to the autopsy report, the buyer was 194 pounds and his instructor weighed in at 256. Add nine gallons of fuel/oil pre-mix to its 526-pound basic empty weight, and they were 31 pounds more than the Pulsar’s stated maximum gross—not much, though more significant in a thousand-pound airplane. But that was the least of the factors conspiring against this flight. The field elevation at South Valley Regional is 4,607 feet msl, and the temperature of 23 degrees Celsius (about 73 Fahrenheit) was well above standard; investigators calculated the density altitude at 6,790 feet. Winds, at least, were favorable, from 150 degrees at 12 knots gusting to 18, and while some small showers were in the vicinity, a pilot who took off immediately afterward to help locate the wreckage said the air was “smooth, without a single bump or downdraft.”
The seller confirmed that while the engine had been run up from time to time, including demonstrations for potential buyers, the airplane hadn’t flown in more than a year. The buyer presumably knew that, and this by itself would have been good reason to contract for a prepurchase. Had he done so, the greatest problem with the aircraft would have come to light almost at once. Heavy soot deposits on the spark plugs showed that the engine was running much too rich, and a teardown by the manufacturer quickly revealed the reasons. The main jets in both carburetors had been replaced with oversized units (180 instead of the stock 165), and the jet needles had been installed too high, so that the fuel mix would have been too rich even with standard jetting—which itself was calibrated for sea-level performance. (Like some motorcycle carburetors, this model increases fuel flow as the throttle opens by pulling a tapered needle up out of a secondary jet. A series of grooves in the top of the needle allows tuners to change its rest setting by mounting the needle in a higher or lower groove. The higher the needle is set, the more fuel flows at any given throttle opening.)
Hindsight is always clearer than foresight—but in retrospect, there were several points at which this accident could have been avoided. Halfway down that 5,860-foot runway, with the airplane laboring unsuccessfully to climb out of ground effect, there was still time to close the throttle and land straight ahead. Before attempting a cross-country in an unfamiliar airplane—particularly one that hadn’t been flown recently—the instructor could have decided to make a test flight solo; weighing 20 percent less, the aircraft’s climb performance might have improved enough to let him get safely around the pattern and land while still raising healthy doubts about the feasibility of the flight. And of course a thorough mechanical inspection prior to purchase would have shown that the engine was not set up for high-altitude operation in the first place.