By David Jack Kenny
The National Transportation Safety Board’s accident investigators are capable of astonishing feats of inference. Wreckage too shattered to offer any obvious hope of reconstructing the preceding chain of events sometimes yields a key bit of evidence that enables them to determine the accident’s cause beyond any reasonable doubt. Occasionally, though, that crucial clue simply isn’t there. If multiple potential failure points can’t conclusively be ruled out, knowing how the crash occurred still doesn’t tell us why.
Thirteen months after a Beech 35-33 Debonair attempted to take off from Runway 27 at Telluride, Colorado, only to fly into a canyon wall half a mile from the departure end and 310 feet below the airport’s elevation, the NTSB officially pronounced the probable cause as “The airplane’s failure to obtain a positive climb rate, which resulted in controlled flight into terrain.” That’s unquestionably true, but it doesn’t provide much guidance as to how to avoid similar tragedies in the future.
At first glance, pilot experience wouldn’t seem to be an issue. All three on board held airline transport pilot certificates, and two—a married couple—were in fact working airline pilots with 12 type ratings between them and a combined 41,000 hours in the cockpit. They had recently joined a flying club based out of Stellar Airpark in the Phoenix suburb of Chandler, Arizona. The Debonair was a club airplane, and the accident flight was part of the wife’s check-out training. (The husband had completed his the week before.) Their instructor, who had served nine years as an Army helicopter pilot, also held a fixed-wing airline transport pilot certificate.
Density altitude was not an issue, although field elevation may have been. The accident occurred on Feb. 16, 2014. The temperature was just at the freezing level, 0 degrees Celsius, with above-standard barometric pressure. Investigators calculated the density altitude as 9,230 feet, just 160 above the airport’s surveyed elevation of 9,070 feet msl. Winds were from the east at 4 knots. Visibility was 1.5 miles in light snow under a broken layer at 1,000 feet and a 1,400-foot overcast. The three had filed an instrument flight plan for their next leg to a planned fuel stop at Cortez, Colorado. After an initial call-up, they taxied to the threshold before obtaining their clearance from flight service.
FAA radar captured three returns, none showing the Debonair climbing significantly along the length of the 7,111-foot runway. Examination of the wreckage found the flaps and gear retracted and ruled out any abnormality in the flight controls. The bending, twisting, and scratching of the propeller blades was consistent with the engine providing at least some power at impact, and it produced compression and spark afterward.
Other facts of immediate interest simply couldn’t be determined. The NTSB’s factual report notes that all available data on pilot experience came from FAA medical applications, making it impossible to assess either instrument currency or make-and-model experience for any of the three. Indeed, it’s not known how recently either of the airline pilots had flown any kind of light airplane before they joined the club. (Some air-carrier professionals continue flying GA throughout their careers. Some don’t.) The husband was 64 years old, putting him within a year of mandatory retirement from his current job.
Based on the airplane’s weight and ambient conditions, the investigators concluded that the Debonair should have been just barely able to manage the 463-feet-per-nautical-mile gradient required by Telluride’s obstacle departure procedure. Instead, it didn’t climb at all. The reported ceilings and visibility suggest that the pilot most likely could see the terrain throughout the takeoff attempt, so a failure to heed the obstacle departure procedure probably wasn’t to blame. However, neither the report itself nor the supporting docket file make any mention of the setting of the mixture control. Post-crash damage and a fire that consumed the cabin may have made it impossible to determine (though that fact itself might have been worth mentioning). Certainly the failure to lean the mixture for best power has figured in other takeoff accidents when low-country pilots have visited high-elevation fields, and the Debonair’s home base lies at just 1,122 feet msl. Between the three of them, they had spent tens of thousands of hours flying turbine-powered aircraft in which fuel mix is not an issue, and flight service had asked them not to call for their clearance until they were No. 1 for departure to avoid delaying other traffic. Running the takeoff checklists in advance of a clearance void time, might they have simply followed the instruction to set “mixture full rich” and moved on? It can’t be ruled out.
Neither can wing contamination; the NTSB report notes that “Investigators were not able to determine what actions the pilots may have taken to remove any snow or ice which may have accumulated on the airplane prior to flight” during the half hour or so they had spent in the FBO. Both might have contributed, and while the tailwind was light, it probably didn’t help.
We don’t know why the Debonair didn’t outclimb the terrain, but we can see a number of chances for supremely experienced pilots to get out of their element without necessarily even realizing it. Going from the massive power reserve of transport-category jets to a piston single, flying it from near sea level to a high-elevation takeoff in instrument conditions in winter, and letting it sit in accumulating snow all offer chances for some important detail to be missed. It would be good to know which (if any) actually was, but that wouldn’t make the principle of double-checking everything any less important.