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By Richard N. Aarons/Business & Commercial Aviation We tend to think of spatial disorientation as something that happens to low-time recreational pilots who stray into IMC and spiral in. Yet spatial disorientation can overtake experienced, high-time pilots as well and can lead to complete loss of control if not remedied immediately. Such was the case on Jan. 27, 2001, when a King Air 200 (N81PF) spiraled out of control and crashed into rolling terrain near Strasburg, Colo., killing both pilots and eight members of the Oklahoma State University basketball team. The airplane, owned by North Bay Charter, LLC, and operated by Jet Express Services, was on an IFR flight plan under CFR Part 91 when the accident occurred. The NTSB's investigation was long and painstaking, ultimately leading to a finding in January that the probable cause "was the pilot's spatial disorientation resulting from his failure to maintain positive manual control of the airplane with the available flight instrumentation." Contributing to the cause, said the Safety Board, "was the loss of AC electrical power during instrument meteorological conditions." The 55-year-old pilot held an FAA ATP certificate, a second-class medical and type ratings in the Cessna Citation and Bombardier Learjet. He was also a certified flight instructor and had accumulated some 5,117 hours total flying time, including 3,650 hours multiengine PIC and 2,520 hours in King Airs. He had flown approximately 51, 13 and 0.4 hours in the 90 days, 30 days and 24 hours, respectively, before the accident. His training and flight checks met all the regulations. The pilot's family told investigators his health had been "good." He was a non-smoker, drank only in moderation and had experienced no significant changes in his personal, professional or financial situation in the previous year. The 30-year-old second pilot essentially was along for the ride. He was not required to be on board for the Part 91 flight nor had he received any formal training in the King Air 200. Nevertheless, he was fairly experienced. He held a commercial certificate, IFR and multiengine ratings, and was an active flight instructor. He had accumulated 1,828 hours total flying time, including 1,218 hours as a multiengine pilot. He had flown approximately 87, 17 and 0.4 hours in the 90 days, 30 days and 24 hours, respectively, before the accident. Friends said the second pilot "wanted to work for an airline and was logging flight time as fast as he could." The Accident The accident airplane was one of three transporting the OSU team to Stillwater Regional Airport (SWO), Stillwater, Okla., after a game at the University of Colorado at Boulder that afternoon.
The pilot had contacted the Denver AFSS about 1100 on the day of the accident to obtain a weather briefing and file IFR flight plans for the return trip to SWO. The briefing included a general synopsis of the weather situation for the proposed flights, AIRMET flight advisories for occasional moderate icing and occasional moderate turbulence, forecast airport conditions, winds and temperatures aloft, and NOTAMs in effect. Generally, the weather in Colorado was IMC with clouds from about 600 feet agl to over 26,000 feet. No icing was reported in the area. A Stevens Aviation ramp worker at Jeffco Airport (BJC) stated that the airplane had been pulled outside from its overnight hangar between 1115 and 1130 on the day of the accident. When the crew arrived at the FBO sometime after 1300, the pilot requested that the airplane be returned to a hangar until after the passengers boarded. The airplane was towed to another hangar, and the pilots left the airport to attend the first half of the basketball game. The crew returned to the airport around 1600 and the pilot contacted BJC ground control at 1631 to obtain an IFR clearance to SWO. (The flight was cleared as filed.) The passengers arrived at BJC at 1700 and boarded the airplane in the hangar. Investigators determined later that the airplane was loaded within its center of gravity limits but about 314 pounds overweight. Stevens personnel towed the airplane to the ramp and the pilot contacted ground control at 1712 for taxi instructions. The controller issued current weather information -- wind was variable at three knots, visibility was one mile in light snow, sky condition was an indefinite ceiling of 200 feet, temperature was -4ºC, dew point was -5ºC -- and a taxi clearance to Runway 29R. About 1717:15, the pilot reported that the airplane was ready to depart from Runway 29R and the BJC controller cleared the flight for takeoff with an instruction to turn right to a heading of 040. About 1719:47, the local controller instructed the pilot to contact the Denver TRACON. At 1719:55, the pilot checked in with the Denver Departure Radar Four position and reported that he was climbing through 6,500 feet to 8,000 feet. The departure controller cleared the flight to climb to 12,000 feet and to fly heading 060. About 1722:09, the controller instructed the pilot to proceed to the EPKEE intersection, join the Garden City transition, and climb to 23,000 feet. The pilot acknowledged the clearance. At 1724:07, the departure controller instructed the pilot to fly the airplane on a 110-degree heading, and the pilot acknowledged this instruction. About 1725:53, the controller instructed the pilot to contact the Satellite Radar Two controller. The pilot contacted the Satellite Radar Two controller at 1726:06, reporting out of 16,300 feet and climbing to 23,000 feet. The controller asked the pilot whether he was flying directly to the EPKEE intersection, and the pilot responded that he had been proceeding to the intersection but had been assigned a heading of 110 degrees. The controller cleared the airplane to proceed directly to the EPKEE intersection. About 1726:27, the pilot stated that he was going directly to the EPKEE intersection and that he needed to make about a three-degree left turn. ATC heard nothing more from the flight. Radar tapes, examined after the accident, showed that the airplane reached its cruising altitude of 23,000 feet at about 1732:35. Investigators determined the airplane's climb through this altitude was normal, and its airspeeds had been steady. The last Mode C transponder return occurred about 1735:44, when the airplane was at an altitude of 23,200 feet; however, Mode A returns continued. Some 42 seconds later, the airplane started to deviate from its heading and turn to the right. Mode A information from the transponder remained available until 1737:12. Within the next five to eight seconds (sometime between 1737:17 and 1737:20) the airplane impacted terrain at an elevation of 5,223 feet some 42 miles east of BJC. The wreckage pattern indicated that the airplane broke up just before impact. All aboard died of multiple blunt force trauma. Despite extreme crash and fire damage to the aircraft structure, NTSB investigators were able to determine that there were no preimpact failures of the airframe, flight controls or powerplants. However, indications recovered from some of the badly damaged cockpit instruments caused investigators to turn their focus to the AC power system. Examination of the crushed pilot-side altimeter revealed that the pre-impact altitude indication was 23,220 feet and that a flag had been visible. This reading suggests that the instrument had lost AC power at cruise altitude and that the AC power had not been reestablished. (The copilot-side altimeter was not recovered.) The RMIs also indicated a cruise-level AC power failure. The pilot-side attitude indicator was damaged by impact forces and fire. Disassembly of the unit showed witness marks that were consistent with a wings-level and an approximately 10-degree nose-down position. The copilot-side attitude indicator was not recovered.
Investigators discovered the AC volt/frequency meter at the accident site after snow had melted almost three months after the crash. The meter face showed two witness marks aligned with the 380-Hz/100-volt position. The No. 1 and No. 2 inverters were found broken, and their internal components and wiring were destroyed. The internal fuses for both inverters were broken but not melted or burned. The inverter select switch, inverter select relay and avionics inverter select relay were not recovered from the wreckage. The circuit breaker panel had broken away from the airplane and showed impact and post-crash fire damage. Almost all of the circuit breakers were found in the open position -- probably due to impact forces. The Safety Board conducted an airplane performance study to develop the time history of the airplane's movement and to calculate various performance parameters. The study revealed that the airplane banked slightly in the right-wing-down direction several seconds after the last Mode C transponder return, the probable time that the pilot lost AC-powered flight instruments. Calculated performance parameters showed that by 1736:15, the airplane's airspeed was about 200 knots, its bank was 30 degrees right-wing down, and its pitch was 15 degrees airplane nose down. Ten seconds later, the airplane started to deviate from its heading and make a right turn to the south. During the next 30 seconds, the airplane's bank angle continued to increase in the right-wing-down direction, and its pitch angle remained near 20 degrees nose down. At 1736:45, the airplane had turned to the north and was continuing its turn to the right. At that point, the airplane's altitude was about 17,200 feet, and its airspeed had accelerated to about 250 knots. The airplane's right bank, nose-down pitch and airspeed continued to increase as the airplane completed a 360-degree rotation in heading by 1737:02. During the time that the airplane was executing the 360-degree turn, its descent rate was increasing constantly to more than 15,000 feet per minute. By 1737:10, the airplane had entered a steep dive and it was descending through 10,000 feet with its pitch angle exceeding 80 degrees nose down and its bank angle exceeding 100 degrees right-wing down. Calculated performance parameters showed that, about the time of the last Mode A transponder return (1737:12), the airplane rolled to the left toward wings level, its descent rate began to be arrested, and its nose-down pitch decreased. During the next five seconds, the airplane's airspeed increased rapidly to more than 350 knots as the descent rate was reduced. The calculated performance parameters also showed that by 1737:15 the airplane was on a 130-degree heading at an altitude of 6,200 feet. A moment later it impacted terrain. Putting It All Together
Ultimately, the investigation team gathered to come up with a coherent explanation of what had happened. It was clear from early in the investigation that the pilot was healthy and properly certificated and qualified under federal regulations. The pilot had filed an IFR flight plan under Part 91 for the accident flight and, as a result, he was the only person responsible for the airplane. As a side issue, the FAA determined in January 2002 that the pilot should have been operating the airplane under Part 135 because he had the primary responsibility for providing the airplane and the pilot services and was receiving compensation for both. The second pilot was properly certificated and qualified under federal regulations; however, the second pilot was not a required flight crewmember because the airplane was certified for single-pilot operation under Part 91. Even if the flight had been operated under Part 135, the second pilot still would not have been a required crewmember -- the airplane was certified for single-pilot operation under Part 135 in IFR conditions because a three-axis autopilot was installed and operating. Safety Board members believe the circumstances of this accident would not have been any different if the pilot had operated the flight under Part 135 rather than Part 91 because the flight was conducted with two qualified pilots and an operational autopilot and thus exceeded Part 135 requirements. The accident airplane was properly certified, equipped and maintained in accordance with federal regulations. IMC prevailed from the surface to altitudes above those of the accident airplane. However, icing was not a factor in this accident. No pilot reports surrounding the time of the accident indicated any inflight icing over Colorado, and none of the pilot witnesses indicated any inflight icing along or near the accident airplane's route of flight. Also, radar data for the accident airplane indicated no degradation of airplane performance (airspeed or altitude) consistent with ice accretion. No evidence of a cabin pressurization problem was found. Radar data indicated that the flight from BJC to SWO was routine until the airplane was at an altitude of 23,200 feet. At that point, the airplane stopped transmitting Mode C altitude transponder information, which is generated from electrical output signals from the airplane's AC-powered air data computer. The airplane continued to transmit Mode A identifying transponder information, which is generated from DC electrical power, until the time of impact. Thus, a total power loss aboard the airplane did not occur, but a partial or complete loss of AC power did occur. Investigators believe it is possible that the AC electrical malfunction involved a failure of the air data computer only. However, the pilot-side altimeter indicated that the altitude reading was 23,220 feet, which was consistent with the last reported altitude (23,200 feet) before the airplane stopped transmitting Mode C information. Also, both radio magnetic indicator (RMI) compass cards showed a heading of 115 degrees, which was consistent with the airplane's heading when Mode C information was lost. In addition, witness marks on the volt/frequency meter showed that it was at the 380-Hz/100-volt position (the lowest reading) at the time of impact, indicating that no AC power was available. The Safety Board concluded that "the physical evidence recovered from the wreckage site and the recorded radar data indicate that a complete loss of AC electrical power occurred aboard the airplane." Further, AC power was not restored any time after it was lost. "If AC power had been restored, the altimeter would have shown an altitude lower than 23,220 feet." The complete loss of AC electrical power, said NTSB investigators, would have rendered most of the pilot's flight instruments inoperative. The only instruments that would have been available to the pilot were those that were operated by the pitot static or vacuum systems. On the left side of the cockpit, only the airspeed indicator and the turn and slip indicator would have been operational. On the right side of the cockpit, the airspeed indicator, turn and slip indicator, altimeter and attitude indicator would have been operational. Despite the loss of the airplane's primary flight instruments, the pilot made no radio transmissions to the controller after Mode C information was lost. (Between one minute, 33 seconds and one minute, 36 seconds elapsed between the time of the last Mode C return and airplane impact.) The airplane's air data computer also produces electrical output signals for the autopilot. Thus, the complete loss of AC power would have caused the autopilot to cease operating if it were being used. The Safety Board was unable to determine from the available evidence whether the pilot was flying the airplane with the autopilot engaged or whether he was flying manually. Ambient cockpit and instrument panel lighting are powered by DC electrical power. Thus, the pilot would have been able to see within the cockpit to attempt to diagnose the electrical problem. The flashing red master warning light and the autopilot disconnect annunciator light would have signaled the loss of the autopilot if it were engaged. Also, instrument flags would have appeared on the pilot's altimeter, attitude indicator, horizontal situation indicator (HSI), radio altimeter, RMI and altitude preselect. "The pilot's experience and recent training should have prepared him to complete all prescribed checklist actions for diagnosing and resolving an electrical system failure," said the Safety Board. "Further, it is possible that the second pilot would have been able to provide some assistance to the pilot. The post-accident examination and testing of a King Air 200 airplane showed that instrument flags would have appeared on the HSI and RMI on the second pilot's [right] side of the cockpit. However, because the second pilot had not received any formal King Air training, he would have had limited experience with the airplane's systems and emergency procedures."
The King Air 200 Pilot's Operating Handbook indicates that if one inverter is inoperative, the other should be selected using the inverter select switch. This switch is located away from other switches on a panel below the instrument panel and to the left of the pilot-side control wheel. The NTSB was unable to determine from the available evidence whether the pilot attempted to restore AC power using the inverter select switch. "Despite the loss of AC electrical power, the pilot could have safely flown and landed the airplane from the left seat by referencing the available [non-AC-powered] flight instruments on the right side of the cockpit [the altimeter and the airspeed, attitude, and turn and slip indicators]," the Board said. "Also, the pilot could have asked the second pilot to fly the airplane because the available flight instruments would be more easily viewed from the right seat." The Board said it could not determine from the available evidence what actions the pilot took (or did not take) and the extent to which the pilot might have coordinated with the second pilot. "Nevertheless, the Safety Board concludes that the pilot did not appropriately manage the workload associated with troubleshooting the loss of AC electrical power with the need to establish and maintain positive control of the airplane." Based on radar returns and performance calculations, the Safety Board concluded that the "airplane's estimated flight path in the final two minutes of flight was consistent with a graveyard spiral resulting from pilot spatial disorientation. "The pilot probably did not sense the right descending turn at first because the airplane's bank was entered gradually. As the airplane's bank angle and descent rate began increasing, the pilot's spatial disorientation most likely persisted, and he was not able to successfully use the available instruments to regain positive control of the airplane. Any head movements that the pilot made while attempting to diagnose the electrical system malfunction [for example, looking down and to the right at the circuit breaker panel] might have exacerbated his spatial disorientation because the motion sensing organs of the inner ear could have been stimulated by these head movements in addition to the motion of the airplane." In a post-accident interview, the air safety inspector who conducted the pilot's March 1998 Part 135 checkride indicated that the pilot tended to "lock in on a problem and not fly the airplane." This observation is consistent with the circumstances of this accident. Radar data, ground scars and wreckage distribution indicated that the airplane impacted terrain at an angle that was less steep than the descent. The Safety Board concluded that the pilot attempted to arrest the descent in the final portion of the flight, possibly in response to obtaining visual references of the ground after emerging from the lowest layer of clouds. "The pilot input and the airplane reaction required to arrest the descent rate with the available altitude would have placed a large aerodynamic loading on the airplane. The aerodynamic loading caused the airplane to break apart in flight at a low altitude [within several hundred feet of the ground] and crash into terrain." Loss of Electrical Power Four possibilities exist to explain the loss of AC power aboard the accident airplane, according to the investigators. First, the selected inverter could have failed, and the pilot might not have switched to the other inverter. However, the pilot should have been familiar with this switch because it is always used to supply AC power after engine start and to terminate AC power before engine shutdown.
Second, a dual inverter failure could have occurred. However, it is extremely unlikely that both inverters would have failed simultaneously because of the inverters' history of reliability aboard King Air 200s. Third, failure of the inverter selector switch, or the inverter select relay, or the avionics inverter select relay could lead to total AC system failure under some circumstances. None of these items was recovered from the wreckage. Fourth, wiring failures, shorts or opens are possible reasons for the loss of AC power. "The Safety Board cannot make a definitive determination regarding what caused the AC electrical system to fail. However, the Safety Board concludes that the AC electrical failure was a contributing factor to this accident but was not a causal factor because non-AC-powered instrumentation remained available for the duration of the flight for the pilot to use to safely fly and land the airplane." Spatial Disorientation The NTSB did not make any recommendations regarding spatial disorientation in its report on this accident "because the FAA has already published many resources to acquaint pilots with the hazards of spatial disorientation." Included on the list of FAA references are: Advisory Circular (AC) 60-4A, "Pilot's Spatial Disorientation"; Aeronautical Information Manual Paragraph 8-1-5, "Illusions in Flight"; Airplane Flying Handbook (FAA-H-8083-3) Chapter 9, "Flight by Reference to Instruments"; Instrument Flying Handbook (FAA-H-8083-15) Chapter 1, "Human Factors"; AC 00-6A, "Aviation Weather"; AC 61-23C, "Pilot's Handbook of Aeronautical Knowledge"; and Medical Facts for Pilots (FAA-P-8740-41). You can find all of these references online at the FAA's Web site -- www.faa.gov. Despite the Board's reluctance to issue a recommendation, the discussion in the report on the phenomenon is worth reading. Spatial disorientation occurs, the NTSB says, when a pilot has inadequate visual information or fails to attend to or properly interpret available information regarding the airplane's pitch and bank. Instead, a disoriented pilot relies on cues that are often misleading. The most hazardous illusions that lead to spatial disorientation result from ambiguous information received from motion-sensing organs located in our inner ears. The sensory organs of the inner ear detect angular accelerations in the pitch, yaw and roll axes and gravity and linear accelerations. During flight, the inner ear organs may be stimulated by motion of the aircraft alone or along with head and body movement. Spatial disorientation can occur in a banked airplane when it rolls very slowly at a rate that is not detected by the motion-sensing organs of the inner ear. The threshold for the detection of roll rate (roll to bank) by humans is about two degrees per second. Spatial disorientation can also occur in a banked airplane when a constant-rate turn is maintained and stimulation of the inner ear organs ceases. A disoriented pilot who falsely perceives a constant-rate turn as a descent may respond with elevator pitch-up controls, which will tighten the turn. As the turn tightens and the airplane's bank continues to increase, the airplane will lose altitude from the resulting loss of vertical lift. A disoriented pilot who still perceives a wings-level flight attitude may respond to the loss of altitude with increased pitch-up controls, resulting in a steep spiral dive (commonly referred to as a "graveyard spiral"). According to the FAA Aeronautical Information Manual, Paragraph 8-1-5, spatial disorientation can be prevented only by visual reference to reliable fixed points on the ground or to flight instruments. FAA AC 60-4A, "Pilot's Spatial Disorientation," states that tests conducted with qualified instrument pilots showed that it could take as long as 35 seconds to establish full control solely by reference to flight instruments when a loss of visual reference occurs. Bottom line -- know your systems and procedures. Practice partial panel. B/CA from this link
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