ERA09FA429

The pilot's improper modification of the certified, on-board oxygen system, which resulted in incapacitation due to hypoxia, and the airplane's subsequent uncontrolled descent into terrain.

The pilot of the single-engine, non-pressurized airplane in cruise flight at 25,000 feet above mean sea level requested and was issued a descent clearance to 12,000 feet. The pilot acknowledged the clearance, but the airplane did not descend. Air traffic control (ATC) noted that the pilot sounded "in distress and out of breath." The pilot was issued the clearance multiple times, but the airplane never descended. The last radio transmission received from the airplane was the pilot's labored breathing. Approximately 1 hour later, the airplane crossed directly over the destination airport at 25,000 feet, and maintained its on-course heading. National Guard aircraft scrambled to intercept the airplane were unable to gain the pilot's attention. The intercepting pilots observed an "unresponsive individual who appeared to be unconscious." The airplane continued in cruise flight at 25,000 feet for another hour after passing the destination airport before it slowed, departed controlled flight, and descended into terrain. All major components of the airplane were accounted for at the accident site. Examination of non-volatile memory from the accident airplane revealed that the onboard oxygen system had 29 percent of its total oxygen capacity remaining when the accident occurred. The airplane was equipped with a factory-installed oxygen system that the pilot had augmented by installing a supplemental pulse-demand oxygen system several months prior to the accident. The manufacturers of both systems explicitly advised against the use of non-original components with their respective systems. The pilot routinely used masks from the airplane's original oxygen system with components from the supplemental system he installed, and even noted the occurrence of a previous encounter with hypoxia in his pilot logbook as a result of this practice.

HISTORY OF FLIGHT On July 30, 2009, at 2149 eastern daylight time, a Cirrus SR-22, N581DS, was destroyed when it impacted terrain in Ravenswood, West Virginia. The certificated airline transport pilot, the sole occupant, sustained fatal injuries. Instrument meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan was filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The flight originated at York Municipal Airport (JYR), York, Nebraska, about 1840, and was bound for Eagle Creek Airpark (EYE), Indianapolis, Indiana. According to the owner of the airplane, who did not hold any pilot certificates, he hired the accident pilot to fly him between JYR and EYE for business during the week. It was their custom to fly at lower altitudes from EYE to JYR, in order to minimize the effects of headwinds. On the return flight to EYE, they would normally fly at 25,000 feet to take advantage of tailwinds. On the day of the accident, he and the accident pilot completed the flight from EYE to JYR at 6,000 feet, and the pilot then departed on the return flight to EYE. The oxygen system was not serviced prior to departure, but was scheduled to be serviced at EYE the following week. Approximately 7 miles northeast of JYR, the pilot contacted Minneapolis Air Route Traffic Control Center and requested an IFR clearance to EYE. The airplane was incrementally cleared to 25,000 feet. Data downloaded from the airplane's Recoverable Data Module (RDM) indicated that the pilot activated the oxygen system at 1852, at 12,160 feet. At 1857, the airplane was cleared to climb from 22,000 feet to 23,000 feet. The pilot acknowledged the instruction, but the controller noted that the pilot's voice had changed, and had taken on a "helium/Mickey Mouse" quality. At 1905, the controller noted that the pilot was "climbing to the wrong altitude" and "stepping all over himself." Later, the airplane was given a vector to avoid traffic, which the pilot acknowledged, but when instructed to proceed on course, the pilot's response was "unreadable." At 1916, the pilot was instructed by air traffic control (ATC) to turn 15 degrees right for traffic. The pilot acknowledged and complied. At 2320, ATC instructed the pilot to proceed on course. The pilot again acknowledged and complied with the instruction. At 1925, the pilot requested a descent to 12,000 feet. The controller stated that the airplane's call sign was "unreadable." After several attempts, the controller verified the airplane as N581DS, and issued a clearance to descend to 24,000 feet. The pilot acknowledged the clearance by responding, "two four zero one delta sierra;" but did not begin a descent. The controller remarked that the pilot sounded "in distress and out of breath." At 1927, the airplane was instructed to descend to 12,000 feet and was issued the altimeter setting. The pilot acknowledged the call and repeated the altimeter setting. However, the airplane maintained cruise flight at 25,000 feet. ATC attempted to contact the airplane for approximately 6 minutes before the pilot responded, at 1934, with, "Go ahead." The airplane was again issued a clearance to 12,000 feet and instructed to "start your descent." An airline pilot on the frequency commented that the accident pilot sounded "incoherent." The last radio transmission received from the airplane, at 1937, was the pilot's labored breathing. At 2051, the airplane crossed directly over EYE at 25,000 feet, and maintained its on-course heading. Data from the RDM revealed that the airplane continued in cruise flight at 25,000 feet until 2146. At that time, after fluctuating for about 30 seconds, engine power and fuel flow parameters dropped to zero, and engine cylinder head and exhaust gas temperatures dropped significantly. The airplane then began to pitch nose-up pitch while decelerating at 25,000 feet, until a sharp, descending left turn was entered. The airplane then continued a string of spiraling left and right turns with changes in nose pitch, both up and down, until the data stream was lost. RDM data also indicated that the oxygen tank was at 29 percent capacity at the time of the accident. The Ohio Air National Guard scrambled aircraft to intercept the accident airplane, but once alongside, the intercepting pilots were unable to gain the pilot's attention visually or by radio. A North American Aerospace Defense Command spokesman stated that the intercepting pilots observed an "unresponsive individual who appeared to be unconscious." The intercepting aircraft remained with the airplane until it departed controlled flight and descended into terrain. PERSONNEL INFORMATION The pilot, age 66, held an airline transport pilot certificate with ratings for airplane single engine and multiengine land; a flight instructor certificate with ratings for airplane single engine, airplane multiengine, and instrument airplane; and a commercial pilot certificate with ratings for rotorcraft and single engine seaplanes. Additionally, he held a Learjet type rating. The pilot reported 18,500 hours of total flight experience on his most recent application for a Federal Aviation Administration (FAA) first-class medical certificate, which was issued on July 14, 2009. On an insurance renewal form dated July 23, 2009, the pilot reported 18,700 total hours of flight experience, 500 hours of which were in the accident airplane make and model. AIRCRAFT INFORMATION The airplane was manufactured in 2008 as a single-engine, unpressurized, composite construction, low-wing airplane. It was equipped with a turbo-normalized, 310-horsepower Teledyne Continental Motors IO-550-N engine. Review of the airplane's maintenance records revealed that the airplane and engine had accrued 445.6 flight hours at the time of the accident. The most recent 100-hour inspection was conducted on July 22, 2009, at a total time of 433.5 hours. Review of the airplane's warranty records revealed an entry dated December 9, 2008, at 145.7 total hours, which stated, "oxygen leaks down to 1600 psi." The work performed entry stated, "Removed tail panel, leak check all fittings found service line at oxygen bottle leaking. Removed line and inspected, no damage to line noted. Reinstalled line secured fittings and serviced oxygen [bottle]." An entry in the airplane's maintenance log, dated January 29, 2009, stated, "Serviced and inspected oxygen fill line for leaks. Tightened line in accordance with aircraft maintenance manual. Serviced oxygen." The most recent oxygen servicing took place on June 10, 2009. METEOROLOGICAL INFORMATION At 2153, the weather reported at Mid-Ohio Valley Regional Airport (PKB), Parkersburg, West Virginia, located approximately 30 miles northeast of the accident site, included winds from 170 degrees at 3 knots, and 2 ½ statute miles visibility in mist. There were scattered clouds at 1,600 feet and 2,600 feet, and a broken ceiling at 3,800 feet. The temperature was 22 degrees Celsius (C), the dew point was 21 degrees C, and the altimeter setting was 29.93. WRECKAGE AND IMPACT INFORMATION The airplane impacted a hill about 6 miles north of the town of Ravenswood, at 39 degrees, 2.07 minutes north latitude, 081 degrees, 44.30 minutes west longitude. The airplane was examined at the site on July 31, 2009. There was an odor of fuel, and all major components were accounted for at the scene. The wreckage path was oriented approximately 115 degrees magnetic, was about 550 feet long, and widened along its length to a width of approximately 150 feet. The first 200 feet of the wreckage path was on the down slope of an open pasture, at the top of a wooded ridgeline. The remainder of the wreckage path was distributed down a steep, heavily wooded incline to a creek bed. A large area of grass just beyond the initial ground scar, and trees along the wood line, exhibited browning of the foliage consisten