Mc Rae, GA, USA
N518SR
Cirrus Design Corp SR22-GTS
The airplane experienced an in-flight loss of aircraft control during cruise flight. The pilot initially reported a turbulence encounter at 9,500 feet, and that he saw damage on the upper surface of both wings. He did not recall a significant loss of altitude or loss of control. Data downloaded from the flight displays after the event indicated that the airplane actually climbed to 15,400 feet above mean sea level (msl), nearly 17,500 feet density altitude, which was the maximum operating altitude for the airplane. The airplane then slowed, stalled, and began a rapid descent, losing 13,000 feet of altitude in about 40 seconds before recovering. During recovery, the airplane had an average of more than 4 Gs vertical loading for more than 20 seconds. Such loading would likely have resulted in G-induced loss of consciousness (G-LOC) or near-loss of consciousness. The pilot's apparent failure to accurately recall the events of the flight is likely a result of the confusion associated with hypoxia, and the subsequent confusion and amnesia associated with G-LOC or near G-LOC. It is unclear exactly why the pilot chose to increase his altitude beyond 12,500 feet msl, above which oxygen use would have been required after 30 minutes. Regardless, he continued to climb the airplane above 14,000 feet msl, an altitude above which oxygen use would have been required by the pilot regardless of the time spent at that altitude, and he subsequently climbed to above 15,000 feet, at which point oxygen use would have been required by all occupants. The pilot confirmed that neither he nor his passengers used supplemental oxygen during the flight. Examination of the airplane found no evidence of mechanical failure or malfunctions that would have prevented the airplane from operating normally.
History Of The Flight On August 21, 2006, about 1341 eastern daylight time, a Cirrus SR22-GTS, N518SR, registered to Wells Fargo Bank, Trustee, and operated by a foreign-certificated private pilot experienced an in-flight loss of aircraft control during cruise flight near Mc Rae, Georgia. The personal flight was operated under the provisions of 14 Code of Federal Regulations (CFR) Part 91 under visual flight rules, with no flight plan filed. Visual meteorological conditions prevailed. The private pilot and two passengers reported no injuries. The airplane was substantially damaged by aerodynamic forces. The flight departed Athens, Georgia, (AHN) on August 21, 2006, at 1246 en route to Fort Lauderdale, Florida. The accident was not reported to the National Transportation Safety Board until October 19, 2006. According to the pilot, the flight departed AHN and was routed to the southeast by Atlanta Center while receiving visual flight rules flight following services. The pilot stated that "we encountered clear air turbulence at approximately 2:00 pm. Bounced once and then after losing altitude hit a very hard bounce of severe turbulence. After stabilizing the airplane my son "... noticed" some thin lines of paint were missing from the top of the right wing, after which I noticed thin lines of paint missing about 6" [inches] in from the fuel filler cap on the left wing. I slowed the plane down to about 90 knots and landed at the nearest airport", which was Telfair-Wheeler Airport, (MQW) Mc Rae, Georgia. "The plane handled with no abnormalities and we landed with no issues." The pilot contacted Cirrus Design Corporation regarding the occurrence. The manufacturer examined the airplane on October 19, 2006, and contacted the Safety Board to report that the airplane had sustained substantial damage. A subsequent telephone interview with the pilot revealed that during the flight, he did not use oxygen. The pilot stated that he believed that his peak altitude was "close to 13,000 feet." He stated that he has used an oxygen system three times on previous trips at altitudes of 13,500 to 14,000 feet and once at 16,000 feet. He said that on those flights, he used a cannula to supply the oxygen to himself and his passengers. He also believed that the autopilot was off just before the aircraft began its descent. He described the airplane as feeling different... "like not flying." He described that the airplane was level and felt kind of like it would feel during a stall, adding that the Cirrus stall was easy to feel coming on, that it was quite noticeable. He stated that he did not hear the stall warning at any time and that the sound it makes was easy to hear. The pilot further stated that neither he nor his passengers were smokers. The pilot did not recall a significant loss of altitude following the turbulence event. Personnel Information The pilot, age 59, held a Federal Aviation Administration (FAA) foreign-based private pilot certificate for airplane single-engine land, issued on August 24, 2001. The foreign-based certificate was issued with the following limits: issued on basis of and valid only when accompanied by Canada pilot license. All limitations and restrictions on the Canada pilot license apply. The pilot held a third-class medical certificate dated September 26, 2005, with a restriction that "Glasses must be worn." According to the pilot, he has accumulated 968 hours total flight time with 876 hours in the Cirrus SR-22. Aircraft Information The four-seat, low-wing, fixed-gear airplane received its standard airworthiness certificate on July 31, 2006. It was powered by a Continental IO-550N, 310-horsepower engine, and equipped with a Hartzell controllable pitch propeller. After landing, the Hobbs/Flight meters indicated 26.7 hours and 21.2 hours respectively. Wreckage and Impact Information Initial visual examination of the airplane's wings revealed damage to the upper skins. The damage appeared as a ridge in the laminate. The wings were removed from the airplane and the paint and foam core were removed from the damaged areas to aid in the examination of the wing. Further examination of the wing revealed that the left upper wing skin was disbanded from the left aft shear web and the right upper wing skin was disbanded from the right aft shear web. The damaged area where the ridge on the right upper wing skin, began at a point about 15 inches outboard of the wing root, and about 4-inches aft of the right leading edge. The damaged area extended aft, about 33.5 inches, along the surface of the wing skin. Additional damage was noted on the lower engine cowling, where a piece of the engine cowling was missing. Several engine cowling mounted screw holes were elongated. The upper and lower engine cowlings exhibited abrasion between the cowling and the fuselage, the cowling-to-cowling mounting points, and between the cowling and propeller spinner. The engine's left front cowling baffle was buckled and a dent was noted in the cross-member of the engine mount. Both flaps were buckled near the mid-flap hinge. Examination of the airframe revealed no evidence of preaccident mechanical malfunctions. Tests and Research Data recovered from the Primary Flight Display (PFD) and the internal compact flash memory card from the Multi-Function Display (MFD) were sent to the Safety Board's Vehicle Recorder Laboratory in Washington, D.C., for examination. The data revealed in summary the following about the flight: About 1246, the airplane departed AHN and climbed to an initial cruise altitude of about 7,500 feet. At that time, the airplane was established on a southerly heading of about 160 degrees and was maintaining a steady climb airspeed of about 130 knots indicated. The airplane reached 7,500 feet at about 1257 and was maintaining an airspeed of about 150 knots indicated. The airplane remained at this altitude until about 1317, when the airplane started a steady climb from 7,500 feet at a rate of approximately 400 feet per minute. During the climb, the indicated airspeed slowly decayed from about 150 knots to a steady 100 knots. At 1329, the airplane leveled off at 13,500 feet. At 1332 the airplane again started to climb to an altitude of about 14,500 feet and leveled off at 1334. The airplane remained at 14,500 until 1338 when it started to climb at a constant rate of about 500 feet per minute. The airplane continued climbing at this rate until 1340 when the airplane leveled off at about 15,400 feet. During the climb the indicated airspeed again started to decrease from 130 knots to about 83 knots at level off. The airplane remained at this altitude but continued to lose airspeed. About 1341 at an indicated airspeed of about 72 knots the airplane pitched down and started into a steep dive. The airplane pitched down to a pitch attitude of about negative 80 degrees. During the dive the airplane rolled to the right about its longitudinal axis through two complete 360 degree revolutions and had started a third revolution, but only attained a +130 degrees of left bank prior to the recovery to straight-and-level flight. The airspeed increased from a low of 72 knots at the start of the dive to a maximum of about 336 knots indicated. Additionally, during the recovery, the airplane sustained a positive "G" loading of 4.733 vertical Gs. (The PFD unit is limited to recording a vertical G-loading of 4.733 Gs even though the actual Gs loading may have been higher). After several positive and negative pitch (+50 degrees nose up to -80 degrees nose down) excursions the airplane ultimately recovered to a straight-and-level flight about 1343. After the initial recovery, the airspeed fluctuated to more than 200 knots after a low of about 120 knots. During the recovery to 2,500 feet, the airplane had lost about 13,000 feet of altitude in about 40 seconds, obtained a maximum airspeed of about 336 knots, and sustained two positive G loadings of at least 4.773 Gs. During the recovery, the recorded data averaged more than 4 Gs for a period of 21 seconds. The airplane never climbed above the recovery altitude of 2,500 feet and landed at MQW about 1401. The entire flight prior to the high-speed dive was smooth and stable. Prior to the upset, the maximum recorded vertical "G" value was about 0.5 Gs centered around neutral. The maximum G value occurred about 1338, when the airplane was at an altitude of 14,500 feet at an airspeed of about 130 knots indicated. According to the Cirrus SR-22 flight manual, the maximum operating altitude for the airplane is 17,500 feet. The flight manual also lists the maximum never exceed (Vne) speed of 201 knots indicated. Additionally, the flight manual lists the flaps up stall (Vs) speed of 70 knots indicated. The airplane was also restricted to a positive G loading, flaps up, of 3.8 Gs and a negative G loading of -1.9 Gs. FAA Regulations, Title 14 CFR 91.211, Supplemental Oxygen states: "...(a) General. No person may operate a civil aircraft of U.S. registry -(1) At cabin pressure altitudes above 12,500 feet mean sea level [msl] up to and including 14,000 feet unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration; (2) At cabin pressure altitudes above 14,000 feet unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes; and (3) At cabin pressure altitudes above 15,000 feet unless each occupant of the aircraft is provided with supplemental oxygen." AC 91-61, A Hazard in Aerobatics: Effects of G-forces on Pilots, notes, in part: Positive Gz Effects. The +Gz induced effects may be described as follows: (1) Grayout. There is graying of vision caused by diminished flow of blood to the eyes. Although there is no associated physical impairment, this condition should serve as a warning of a significant impairment of blood flow to the head. (2) Blackout. Vision is completely lost. This condition results when the oxygen supply to the light sensitive retinal cells is severely reduced. Contrary to other common usages of the term, consciousness is maintained. In blackout, some mental activity and muscle function remains, thus the occurrence of blackout warns of seriously reduced blood flow to the head and of a high risk of loss of consciousness. Note: In some centrifuge studies, 50 percent of the pilots had simultaneous blackout and loss of consciousness. Therefore, a pilot cannot rely on blackout to precede loss of consciousness. (3) Loss of Consciousness. When the blood flow through the brain is reduced to a certain level, the pilot will lose consciousness. He or she may have jerking, convulsive movements; these have been seen in many subjects of centrifuge studies and in some pilots during actual flight. The pilot will slump in his or her seat. Possibly, the pilot will fall against the controls, causing the aircraft to enter flight configurations from which it cannot recover even if consciousness is regained. In centrifuge studies, many pilots lost (and regained) consciousness without realizing they had done so. (4) How long does induced unconsciousness last? In a series of studies of pilots in centrifuges, the pilots were unconscious for an average of 15 seconds. Following this, there was an additional 5 to 15 second interval of disorientation. Thus, if there is loss of consciousness due to +Gz forces, there will be a 20 to 30 second (or longer) period during which the pilot is not in control of his or her aircraft. According to a textbook of aerospace medicine (Gradwell DP. Hypoxia and Hyperventilation. In: Ernsting's Aviation Medicine, 4th edition (eds. DJ Rainford and DP Gradwell). Edward Arnold, London, 2006. p. 53.), "Even in the resting subject, the symptoms and signs of hypoxia appear on acute exposure to altitudes greater than 15,000 feet when breathing air. Higher mental processes and neuromuscular control are affected; in particular, there is a loss of critical judgment and willpower. Because of the loss of self-criticism, the subject is usually unaware of any deterioration in performance or indeed of the presence of hypoxia; it is this that makes the condition such a potentially dangerous hazard in aviation. Thought processes are slowed, mental calculations become unreliable, and psychomotor performance is grossly impaired."
The pilot's failure to use supplemental oxygen where required, and his failure to maintain sufficient airspeed to avoid a stall.
Source: NTSB Aviation Accident Database
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