Aircraft Accident/Incident Report

Lander, Wyoming 82520
Monday, October 25, 2010 13:52 MDT

The owner/pilot and his three sons flew in the single engine, normally aspirated airplane from the Minneapolis, Minnesota, area to Jackson, Wyoming, to attend a family function. The return trip was planned for Sunday, but the pilot canceled that flight due to winter weather conditions. Also due to weather concerns, he booked a Monday return to Minnesota via commercial airline. However, that commercial flight was canceled for non-weather reasons, and the pilot chose to return in his airplane. He contacted flight services twice by telephone to obtain weather briefings and filed a flight plan. Both weather briefings included AIRMETs for mountain obscuration, turbulence, and icing along the planned flight route and altitude. About 2 hours after the second call, the pilot filed a second instrument flight rules (IFR) flight plan by computer, with a proposed departure time 10 minutes after the filing time. About 20 minutes after filing, the pilot was issued a clearance that differed from the one he had requested. The differences included a departure to the south instead of the north, an off-airway segment, and a clearance altitude 5,000 feet higher than originally requested. The assigned altitude was lower than and counter to Federal Aviation Administration (FAA) published requirements for the area in which the pilot was flying, but neither the pilot nor the controller questioned the altitude assignment. The airplane departed 8 minutes after the clearance was issued. About 30 minutes after takeoff, when the airplane was on the off-airway segment, radar coverage from the Rock Springs Air Route Surveillance Radar was lost because the system at the FAA facility that was handling the airplane was intentionally made unavailable to controllers due to data reliability concerns. However, controllers at another FAA facility that was not handling the airplane continued to successfully use that same data. Four minutes later, the pilot filed a report with flight services that he was encountering light turbulence and a trace of rime icing. About 6 minutes later, the airplane was reacquired by ground radar. The controller then asked the pilot to climb to 16,000 feet, the minimum IFR altitude in that sector. Two minutes later, the pilot reported that he might not be able to reach 16,000 feet. About 2 minutes after that, the pilot reported that he was in a "severe mountain wave," and that he was "descending rapidly." There were no further communications from or radar targets associated with the airplane. The wreckage was located 7 days later, at an elevation of about 11,000 feet. Damage patterns were consistent with impact while the airplane was in a left spin. Examination of the engine and airframe did not reveal any preexisting mechanical deficiencies or failures that would have precluded normal operation. The pilot appeared intent on returning home that day and had made alternate travel plans, which were foiled for reasons beyond his control. His repeated checks of the weather and multiple flight plans indicated that he was attempting to take advantage of the continuously changing conditions and depart in his airplane as soon as a short-term window of opportunity arose. This self-imposed time pressure, coupled with his lack of recent IFR experience, likely resulted in his acceptance of the non-conforming clearance. While the pilot was responsible for accepting a clearance that did not comply with minimum instrument altitude requirements, air traffic control (ATC) services were deficient in not ensuring that the clearance complied with FAA requirements. The controller should have been aware of the minimum instrument altitudes in his area of responsibility and ensured compliance with them. The decision of the FAA facility handling the airplane to not utilize certain radar data diminished the performance of the minimum safe altitude warning system by preventing the system from detecting a hazardous situation and depriving the controller of a timely altitude alert, which might have enabled him to better assist the pilot. The airplane took off at or near its maximum certificated gross weight. Although the information was available to him, the pilot was either unaware of or discounted the fact that the clearance route that he was issued and accepted required a minimum altitude near the performance limits of the airplane, and that altitude was significantly higher than the altitude he had requested. The altitudes filed for by the pilot and assigned by ATC were also above the freezing level and in forecast icing conditions. The assigned altitude also required supplemental oxygen for all four persons on board, but the onboard system was only configured for two persons. Meteorological information indicated that IFR conditions, turbulence, and icing were likely present in the vicinity of the descent, and possibly more significant than previously reported by the pilot. It could not be determined whether the airplane was actually in a mountain wave, but the pilot was unable to arrest the airplane’s descent. Those factors, combined with the small difference between the airplane's stall speed and best climb speed, likely resulted in the stall and subsequent spin of the airplane. Although it would not have aided the airplane occupants in this case, if the airplane had been equipped with a 406-MHz emergency locator transmitter, it is likely that the time and resources expended to locate the wreckage would have been significantly reduced. Based on the findings of this accident, the NTSB issued three safety recommendations to the FAA. Safety recommendation A-11-32 asked the FAA to “establish Standard Instrument Departure procedures that provide transition routes and minimum instrument flight rules altitude information for aircraft cleared over commonly used navigational fixes from Jackson Hole Airport and similarly situated airports.” The FAA has established standard instrument departure procedures with minimum altitude information for Jackson Hole Airport and continues to survey other mountainous airports; thus, safety recommendation A-11-32 is classified “Open—Acceptable Response.” Safety recommendation A-11-33 asked the FAA to “modify en route automation modernization software such that en route minimum safe altitude warning alerts are provided for aircraft in coast track status that are receiving automatic position updates.” Safety recommendation A-11-34 asked the FAA to “modify en route automation modernization software such that cautionary warnings are provided to controllers when an aircraft is predicted to enter a minimum instrument flight rules altitude (MIA) polygon below the MIA.” The FAA is researching whether the en route automation modernization software can be modified to address safety recommendations A-11-33 and -34, which are classified “Open—Acceptable Response.”

The pilot's decision to depart into known adverse weather conditions over mountainous terrain, which required operation near the limits of the airplane's performance capability and which resulted in a loss of airplane control and subsequent ground impact. Contributing to the accident was an improper clearance issued by the air traffic controller and the pilot's acceptance of that clearance. Also contributing to the accident was the extended loss of radar data from the Rock Springs Air Route Surveillance Radar, which caused loss of radar contact and consequent loss of minimum safe altitude warning protection for the flight.