Amarillo, TX, USA
N933DC
PILATUS AIRCRAFT LTD PC 12
The pilot and two medical crewmembers departed on an air ambulance flight in night instrument meteorological conditions to pick up a patient. After departure, the local air traffic controller observed the airplane's primary radar target with an incorrect transponder code in a right turn and climbing through 4,400 ft mean sea level (msl), which was 800 ft above ground level (agl). The controller instructed the pilot to reset the transponder to the correct code, and the airplane leveled off between 4,400 ft and 4,600 ft msl for about 30 seconds. The controller then confirmed that the airplane was being tracked on radar with the correct transponder code; the airplane resumed its climb at a rate of about 6,000 ft per minute (fpm) to 6,000 ft msl. The pilot changed frequencies as instructed, then contacted departure control and reported "with you at 6,000 [ft msl]" and the departure controller radar-identified the airplane. About 1 minute later, the departure controller advised the pilot that he was no longer receiving the airplane's transponder; the pilot did not respond, and there were no further recorded transmissions from the pilot. Radar data showed the airplane descending rapidly at a rate that reached 17,000 fpm. Surveillance video from a nearby truck stop recorded lights from the airplane descending at an angle of about 45° followed by an explosion. The airplane impacted a pasture about 1.5 nautical miles south of the airport, and a postimpact fire ensued. All major components of the airplane were located within the debris field. Ground scars at the accident site and damage to the airplane indicated that the airplane was in a steep, nose-low and wings-level attitude at the time of impact. The airplane's steep descent and its impact attitude are consistent with a loss of control. An airplane performance study based on radar data and simulations determined that, during the climb to 6,000 ft and about 37 seconds before impact, the airplane achieved a peak pitch angle of about 23°, after which the pitch angle decreased steadily to an estimated -42° at impact. As the pitch angle decreased, the roll angle increased steadily to the left, reaching an estimated -76° at impact. The performance study revealed that the airplane could fly the accident flight trajectory without experiencing an aerodynamic stall. The apparent pitch and roll angles, which represent the attitude a pilot would "feel" the airplane to be in based on his vestibular and kinesthetic perception of the components of the load factor vector in his own body coordinate system, were calculated. The apparent pitch angle ranged from 0° to 15° as the real pitch angle steadily decreased to -42°, and the apparent roll angle ranged from 0° to -4° as the real roll angle increased to -78°. This suggests that even when the airplane was in a steeply banked descent, conditions were present that could have produced a somatogravic illusion of level flight and resulted in spatial disorientation of the pilot. Analysis of the performance study and the airplane's flight track revealed that the pilot executed several non-standard actions during the departure to include: excessive pitch and roll angles, rapid climb, unexpected level-offs, and non-standard ATC communications. In addition to the non-standard actions, the pilot's limited recent flight experience in night IFR conditions, and moderate turbulence would have been conducive to the onset of spatial disorientation. The pilot's failure to set the correct transponder code before departure, his non-standard departure maneuvering, and his apparent confusion regarding his altitude indicate a mental state not at peak acuity, further increasing the chances of spatial disorientation. A postaccident examination of the flight control system did not reveal evidence of any preimpact anomalies that would have prevented normal operation. The engine exhibited rotational signatures indicative of engine operation during impact, and an examination did not reveal any preimpact anomalies that would have precluded normal engine operation. The damage to the propeller hub and blades indicated that the propeller was operating under high power in the normal range of operation at time of impact. Review of recorded data recovered from airplane's attitude and heading reference unit did not reveal any faults with the airplane's attitude and heading reference system (AHRS) during the accident flight, and there were no maintenance logbook entries indicating any previous electronic attitude director indicator (EADI) or AHRS malfunctions. Therefore, it is unlikely that erroneous attitude information was displayed on the EADI that could have misled the pilot concerning the actual attitude of the airplane. A light bulb filament analysis of the airplane's central advisory display unit (CADU) revealed that the "autopilot disengage" caution indicator was likely illuminated at impact, and the "autopilot trim" warning indicator was likely not illuminated. A filament analysis of the autopilot mode controller revealed that the "autopilot," "yaw damper," and "altitude hold" indicators were likely not illuminated at impact. The status of the "trim" warning indicator on the autopilot mode controller could not be determined because the filaments of the indicator's bulbs were missing. However, since the CADU's "autopilot trim" warning indicator was likely not illuminated, the mode controller's "trim" warning indicator was also likely not illuminated at impact. Exemplar airplane testing revealed that the "autopilot disengage" caution indicator would only illuminate if the autopilot had been engaged and then disconnected. It would not illuminate if the autopilot was off without being previously engaged nor would it illuminate if the pilot attempted and failed to engage the autopilot by pressing the "autopilot" pushbutton on the mode controller. Since the "autopilot disengage" caution indicator would remain illuminated for 30 seconds after the autopilot was disengaged and was likely illuminated at impact, it is likely that the autopilot had been engaged at some point during the flight and disengaged within 30 seconds of the impact; the pilot was reporting to ATC at 6,000 ft about 30 seconds before impact and then the rapid descent began. The airplane was not equipped with a recording device that would have recorded the operational status of the autopilot, and the investigation could not determine the precise times at which autopilot engagement and disengagement occurred. However, these times can be estimated as follows: • The pilot likely engaged the autopilot after the airplane climbed through 1,000 ft agl about 46 seconds after takeoff, because this was the recommended minimum autopilot engagement altitude that he was taught. • According to the airplane performance study, the airplane's acceleration exceeded the autopilot's limit load factor of +1.6g about 9 seconds before impact. If it was engaged at this time, the autopilot would have automatically disengaged. • The roll angle data from the performance study were consistent with engagement of the autopilot between two points: 1) about 31 seconds before impact, during climb, when the bank angle, which had stabilized for a few seconds, started to increase again and 2) about 9 seconds before impact, during descent, at which time the autopilot would have automatically disengaged. Since the autopilot would have reduced the bank angle as soon as it was engaged and there is no evidence of the bank angle reducing significantly between these two points, it is likely that the autopilot was engaged closer to the latter point than the former. Engagement of the autopilot shortly before the latter point would have left little time for the autopilot to reduce the bank angle before it would have disengaged automatically due to exceedance of the normal load factor limit. Therefore, it is likely that the pilot engaged the autopilot a few seconds before it automatically disconnected about 9 seconds before impact. The operator reported that the airplane had experienced repeated, unexpected, inflight autopilot disconnects, and, two days before the accident, the chief pilot recorded a video of the autopilot disconnecting during a flight. Exemplar airplane testing and maintenance information revealed that, during the flight in which the video was recorded, the autopilot's pitch trim adapter likely experienced a momentary loss of power for undetermined reasons, which resulted in the sequence of events observed in the video. It is possible that the autopilot disconnected during the accident flight due to the pitch trim adapter experiencing a loss of power, which would have to have occurred between 30 and 9 seconds before impact. A postaccident weather analysis revealed that the airplane was operating in an environment requiring instruments to navigate, but it could not be determined if the airplane was in cloud when the loss of control occurred. The sustained surface wind was from the north at 21 knots with gusts up to 28 knots, and moderate turbulence existed. The presence of the moderate turbulence could have contributed to the controllability of the airplane and the pilot's inability to recognize the airplane's attitude and the autopilot's operational status.
HISTORY OF FLIGHTOn April 28, 2017, about 2348 central daylight time, a Pilatus PC-12 airplane, N933DC, impacted terrain near Rick Husband Amarillo International Airport (AMA), Amarillo, Texas. The airline transport pilot and the two medical flight crewmembers were fatally injured. The airplane was destroyed. The airplane was registered to and operated by Rico Aviation LLC under the provisions of Title 14 Code of Federal Regulations (CFR) Part 135 as an air ambulance flight. Instrument meteorological conditions prevailed at the time of the accident, and the flight was operated on an instrument flight rules (IFR) flight plan. The flight was originating at the time of the accident and was en route to Clovis Municipal Airport (CVN), Clovis, New Mexico. The AMA-based flight crew was first notified of an air ambulance mission by the Rico Aviation medical dispatcher at 2248. The mission was to transport a patient from Clovis, New Mexico, to Lubbock, Texas. The mission was delayed until receiving arrangements were made for the patient at the destination medical facility. During the delay, the pilot continued his flight preparation, including requesting and receiving his air traffic control (ATC) clearance. A review of Federal Aviation Administration (FAA) ATC data revealed that, at 2332:15, the pilot contacted AMA ground control, said that he had received automatic terminal information service Oscar, and requested an IFR clearance to CVN. At 2332:40, the ground controller issued the pilot a clearance to CVN "as filed" with a climb to a final altitude of 8,000 ft mean sea level (msl); the assigned transponder code was 4261. The pilot correctly read back the clearance. Final acceptance of the mission by the Rico Aviation medical dispatcher and the pilot came at 2334. The pilot contacted AMA ground control at 2341:54 and requested to taxi to the runway for departure. The ground controller instructed the pilot to taxi to runway 4. At 2343:50, the local controller cleared the flight for takeoff and instructed the pilot to turn right on course after departure. The pilot acknowledged the takeoff clearance and instructions. After departing runway 4, the local controller observed a primary target with an associated transponder code of 4254, which was the code that had been assigned to the airplane on its previous flight. The local controller observed the 4254 target climb through 4,400 ft msl and instructed the pilot to reset the transponder to 4261. The pilot reset the transponder code to 4261. The local controller observed the beacon code change from 4254 to 4261, then advised the pilot "I've got you now," and instructed him to contact AMA departure control. At 2346:54, the pilot contacted AMA departure control and reported "with you at 6,000 [ft msl]." The west radar departure controller radar-identified the airplane. At 2348:12, the departure controller advised the pilot that he was no longer receiving the airplane's transponder; the pilot did not respond. The departure controller made three more transmissions to the pilot without response. There were no further recorded transmissions to or from the airplane. The local controller reported to the departure controller that he had observed a fireball and reported a potential crash. Figure 1 shows the plotted AMA radar data illustrating the accident flight path. The red targets are from transponder code 4254, and the blue targets are from transponder code 4261. The last eight recorded targets are labeled with their mode C reported altitudes. Figure 1 – Plotted radar data illustrating the accident flight path Surveillance video from a nearby truck stop, located about 400 yards southwest of the accident site, recorded lights from the airplane followed by an explosion. Still images were taken from the video and layered to produce figure 2, which depicts the airplane's final flight path. The images show the airplane descending about a 45°angle to ground impact. Figure 2 – Accident airplane's final flight path PERSONNEL INFORMATIONThe pilot-in-command (PIC), age 57, had been employed at Rico Aviation since November 2016. While employed at Rico Aviation, he had flown with the company's director of operations (DO), the chief pilot, and the contracted flight instructor who trained Rico Aviation pilots in the PC-12, none of whom reported any concerns or issues with the pilot's flying skills. They also stated that there were no difficulties during the pilot's PC-12 training. For Pilatus PC-12 airplane-specific ground and flight training, Rico Aviation contracted with ACFT Services, LLC. Rico Aviation training records did not show the dates of the PC-12 ground training that ACFT Services provided to the pilot. Rico Aviation records indicated that the pilot's initial flight training in the PC-12 occurred between October 26 and 28, 2016, and was conducted by the ACFT Services instructor. ACFT Services issued the pilot a certificate of completion of training dated October 28, 2016. The training records showed satisfactory completion of maximum rate climbs, stalls in multiple configurations, and unusual attitude recovery. Also, high speed descents were discussed during this training. Further flight training was provided by the Rico Aviation DO on December 14, 2016, and by the Rico Aviation chief pilot on November 15, 2016, and December 15, 2016. Autopilot Use, Procedures, and Training According to the ACFT Services instructor who provided the PC-12 flight training to the pilot, pilots were taught to follow the manufacturer's limitation as to when to engage the autopilot after takeoff. The PC-12 airplane flight manual stated that the autopilot must not be engaged when the airplane is below 1,000 ft above ground level (agl). The standard procedure at Rico Aviation, confirmed by the Rico Aviation chief pilot, was to engage the autopilot at 1,000 ft agl after takeoff or when comfortably established in the climb. The chief pilot had flown with the accident pilot on several occasions and had provided flight instruction to him in preparation for his Part 135 proficiency check, which was completed on December 21, 2016. He stated that the pilot used the autopilot normally and showed good knowledge of the autopilot but could fly fine without it. The Rico Aviation training records indicated that the DO had flown with the pilot 7 days before the pilot's proficiency check. The DO stated that he had also flown with the pilot after the pilot's proficiency check as well as about a month before the accident on a repositioning flight. During these flights, he noticed no areas in which the pilot needed extra training. He thought the pilot would rather hand-fly the airplane than use the autopilot. The DO, the chief pilot, and a medical crewmember all reported that they had not heard any negative comments from other Rico Aviation employees about the pilot's performance. The medical crewmember and the chief pilot each reported no known personal or medical issues that could have affected the pilot's performance. The pilot's logbooks were not recovered during the investigation, and the pilot's recent flight experience was obtained from the Rico Aviation PC-12 airplane flight logs, which were kept at the company's Amarillo base. The pilot had flown 28 hours in the preceding 90 days and 115 hours in the last year, 73 hours of which were in the PC-12. A review of the pilot's duty records from the operator indicated he had 4.2 hours of IFR flight time in the preceding 90 days, with 1.4 hours of this time at night. The pilot had accumulated a total of 2.6 hours of night IFR time, and 5.9 hours total IFR time since his last instrument proficiency check on December 21, 2016. Pilot's Preaccident History The pilot worked the night shift, from 1900 to 0800, on April 25th through April 28th and had logged 2 hours during those 3 shifts; he rotated between the Amarillo base and the Dalhart base during those dates. While on duty in Amarillo, he stayed at the Rico Aviation hangar at AMA. While on duty in Dalhart, he stayed at a crew house. When off-duty in Amarillo, he stayed at a local motel. The chief pilot stated that the pilot had checked out of the motel the morning of April 28, and he had no knowledge of the pilot's activities during the day. In correspondence with the pilot's wife, who resided in another state, she reported that the pilot did not have any problems adapting to the overnight duty schedule. She stated that he would sleep during the day and stay awake when on duty overnight. When preparing to start an overnight duty schedule, he would acclimate to that sleep/work schedule 1 or 2 days before. She was not aware of any sleep or health issues relating to his schedule. In the 3 days before the accident, she reported nothing unusual or out-of-the ordinary in any of her routine daily contacts with the pilot. AIRCRAFT INFORMATIONAirplane Background Information The airplane was a nine-passenger, single-engine, turboprop airplane. It was configured as an air-ambulance with pilot and copilot seats, four seats in the cabin, and a patient bed. According to the last available flight logs, the airplane had accumulated 4,466.9 total hours and 3,769 total cycles. Airplane Maintenance Information According to the company's FAA-issued operations specifications, Rico Aviation was to maintain aircraft that were type-certificated with nine or fewer passenger seats in accordance with the manufacturer's maintenance documents and 14 CFR Parts 43, 91, and 135. All maintenance, preventive maintenance, and alterations to the aircraft, engines, propeller, and appliances were to be performed in accordance with current FAA regulations; manufacturer's service manuals, recommendations, and specifications; manufacturer's service bulletins and service letters; and airworthiness directives. Chapters 4 and 5 in the Pilatus PC-12/45 Aircraft Maintenance Manual (AMM) contained the maintenance intervals for each airworthiness limitation item, 100-hour inspection, annual inspection, supplemental structural inspections, and progressive inspection requirements. On March 2, 2017, a set of routine maintenance inspections and tasks was accomplished at an airplane total time of 4,407.5 hours and 3,658 total cycles. In addition to the routine maintenance inspections and tasks, 21 discrepancies (non-routine items) were corrected during this maintenance visit, including the following item: Autopilot disconnecting on approaches – Removed Autopilot Computer P/N 065-0064-15, S/N 2175. Installed "Modified" Autopilot Computer P/N 065-0064-15, S/N X1898 There was one additional log entry for an autopilot discrepancy reported by a Rico Aviation pilot on April 26, 2017: Autopilot disconnects on climb and cruise. Maintenance troubleshot the system and suspect Autopilot Trim Adapter to be causing issue. Removed Autopilot Trim Adapter P/N: 065-00164-0100, S/N: 1745. Installed Tested Autopilot Trim Adapter (KTA336-100) P/N 065-00164-0100, S/N: 1794. System ops check good. All work performed in accordance with the Pilatus PC-12 Maintenance Manual Ch. 22-10-07. The maintenance records did not reveal any write ups or logbook items indicating any issues with the electronic attitude director indicator (EADI) or attitude and heading reference system (AHRS). For a full list of the maintenance completed see the Maintenance Factual Report in the public docket associated with this report. Autopilot System Description The PC-12's primary flight control system for pitch, roll, and yaw is controlled by push-pull rods and/or cables. The secondary flight control system for roll and yaw consists of electrically-actuated trim tabs installed on the primary flight control surfaces; for pitch, the horizontal stabilizer is trimmed electrically. Trim positions for pitch, roll, and yaw are visually depicted on a triple trim indicator on the center console. The horizontal stabilizer, rudder, and aileron trim systems share a trim interrupt switch, which, if pressed due to a trim runaway of any of the respective systems, disconnects power from the pitch trim adapter and the aileron, rudder, and horizontal stabilizer trim actuators. The rocker-type switch is installed on the center pedestal and protected by a safety cover. The two-position switch is labeled "INTR" for the interrupt position and "NORM" for the normal position. The airplane was equipped with a Honeywell (formerly Bendix/King) KFC-325 digital automatic flight control system (AFCS), which provided 3-axis (pitch, roll, and yaw) control. This system provided flight director guidance, autopilot functionality, and autopilot system monitoring. According to Honeywell, the system consists, in part, of a single KCP 220 autopilot computer, a mode controller, an altitude preselector, a pitch trim adapter, pitch, roll, and yaw servo-actuators, a control wheel steering (CWS) switch, a go-around switch, an autopilot disconnect switch, an EADI, and an electronic horizontal situation indicator. The autopilot computer processes flight environment and navigation data from a variety of sensors to compute pitch and roll steering commands. The pilot provides input to the AFCS through the KMC 321 mode controller, located on the forward instrument panel. The AFCS requires the successful completion of a pilot-activated preflight test (PFT) as a prerequisite for autopilot mode engagement. A momentary depression of the self-test button on the mode controller will start a 5-second check of the functionality of the autopilot system, the auto trim system, including the KTA 336 trim adapter, and their system monitors. Indications to the pilot of successful PFT completion is four flashes of the "TRIM" caption on the mode controller as the system is driven twice in each direction with the drive request being interrupted. This operation simulates a trim runaway and checks the ability of both monitors to detect it. After the test sequence, the aural warning tones are annunciated, and the autopilot annunciator on the mode controller flashes twelve times. If the PFT circuit detects a failure, the red "TRIM" caption on the mode controller stays on, and the red "A/P TRIM" warning on the Central Advisory and Warning System (CAWS) display unit illuminates. After the successful completion of the PFT, the autopilot can be engaged by the pilot during flight by depressing the "AP" pushbutton on the mode controller. The autopilot will disengage when any of the following occur: On the mode controller, the "AP" pushbutton is pushed to turn off the autopilot. On the control wheels, the "A/P DISC" pushbutton is pushed. The trim trigger on either control wheel is depressed (manual trim engaged). The trim interrupt switch is pushed. The alternate stabilizer trim switch is set to "UP" or "DOWN." A loss of power to the autopilot computer or the trim adapter occurs. The monitors within the autopilot computer detect a failure. The following autopilot monitor limit(s) are exceeded: Roll rates more than 10° per second (Except when the CWS switch is held depressed.) Pitch rates more than 5° per second (Except when the CWS switch is held depressed.) Accelerations outside of a +1.6g to +0.3g envelope (Disengagement will take place regardless of whether the CWS switch is activated.) When the autopilot is disengaged, manually by the pilot or automatically when a problem is detected, the following captions and warnings are displayed: On the mode controller, the "AP" caption flashes four times then turns off. On the CAWS display unit, the amber "A/P DISENG" caution message will illuminate 3 seconds after the signal input to the CAWS changes from 28V (autopilot engaged) to 0V (autopilot disengaged) and the CWS button is not pressed. The caption will remain illuminated for about 26 to 27 seconds; it extinguishes at a maximum of 30 seconds from the initial time of the autopilot disconnect. On the EADI, the red "AP" caption flashes five times then turns off. The autopilot disconnect warning tone
The pilot's loss of airplane control due to spatial disorientation during the initial climb after takeoff in night instrument meteorological conditions and moderate turbulence.
Source: NTSB Aviation Accident Database
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