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Mystery crash kills threeMystery crash kills three

(DFW08FA111)(DFW08FA111)

Some aircraft accidents make you wonder what the pilot could have been thinking. Others just leave you wondering what happened.

A little before 4 p.m. on April 22, 2008, several people fishing in the Toledo Bend Reservoir along the Texas-Louisiana border heard the sound of an airplane engine. They described it to investigators as “cutting out, sputtering or stalling.” The airplane itself was obscured by clouds until it descended nose-down into the water. The pilot made no apparent attempt to arrest the descent. Boaters hurried to the scene, called 911 with the GPS coordinates, and collected floating debris, but there were no survivors. The impact shattered the Cirrus SR22, which sank in 40 feet of water.

The flight had left Tupelo, Miss., about two hours earlier on an instrument flight plan to the David Wayne Hooks Airport in Houston. On board were the instrument-rated private pilot and two passengers. Twenty minutes after takeoff the pilot requested and received clearance to climb to 10,000 feet, then was given a frequency change. At 2:16 p.m., he advised Memphis Center that he was level at 10,000 feet. His readback of the altimeter setting was ATC’s last radio contact with the flight; the next frequency change, given 33 minutes later, was never acknowledged.

Radar data showed that the airplane continued straight and level at 10,000 feet msl for almost another hour. At 3:49 p.m., it suddenly turned right and descended rapidly until radar contact was lost. The NTSB investigator calculated that this was just about the time the fuel tank in use would have run dry if the pilot hadn’t changed tanks during the flight.

The reservoir is a flooded river valley that borders the Sabine National Forest. The bottom is a tangle of tree trunks, some fallen and some still rooted. Silt three feet deep has accumulated on its floor. Divers made three separate attempts to retrieve the scattered wreckage and eventually located components including the engine and propeller, both main landing gear, fragments of the wings and control surfaces, and the CAPS ballistic parachute, still stowed in its bag. However, the main section of the fuselage, including the cockpit and instrument panel, was never found.

The NTSB noted that the flight track was consistent with the airplane flying on autopilot until the tank ran dry. When the airspeed began to decay, the autopilot would have pitched up to maintain altitude until the airplane stalled. Incapacitation of the crew seemed plausible, particularly since the activation handle to deploy the parachute is accessible from all four seats.

Maintenance records showed that the exhaust header for the number six cylinder had cracked and been replaced three times in a little more than a year, most recently four months before the accident. The temperature at 10,000 feet was estimated at about 8 degrees Celsius, or 46 F. The report pointed out that the airplane’s standard equipment did not include a carbon monoxide detector. However, it was impossible to tell whether an aftermarket detector was in the cockpit or whether the cabin heat had been in use. The exhaust system and all other accessories were stripped from the engine by the impact, and the FAA toxicology lab “did not receive adequate specimens to perform testing for the presence of carbon monoxide.” The accident was officially attributed to “A loss of control for undetermined reasons.”

Eighty percent of all accidents resulting from physical incapacitation of the pilot are fatal. Those definitively attributed to carbon-monoxide poisoning have been rare—just 10 in 20 years. But there’s little doubt that it played a role in a number of crashes that have never been explained, and it’s a risk factor well within the pilot’s control. Minimizing use of the cabin heat isn’t an unreasonable precaution. Periodic cold blasts from the fresh-air vents can help clear the head, letting you know that it was getting foggy to begin with—and a disposable carbon-monoxide detector is very cheap insurance. No one can say whether it would have saved lives in this case. But basic precautions to guard against carbon monoxide poisoning can help prevent this rare but deadly cause of incapacitation.

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