Pilot Debrief

Air Tractor AT502 near Grant, NE — 2020-07-25

Final reportCEN20LA306
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Date
2020-07-25
Location
Grant, NE, USA
Aircraft
Air Tractor AT502
Registration
N502KJ
Category
Airplane
Highest injury
Fatal
Fatalities
1
Phase of flight
Maneuvering

Probable cause

The pilot’s exceedance of the airplane’s critical angle of attack while maneuvering during an agricultural flight, which resulted in an aerodynamic stall and a loss of control at too low of an altitude to recover. Contributing to the accident was the pilot’s excessive climb technique between spray passes.

Contributing factors

Contributing to the accident was the pilot’s excessive climb technique between spray passes.

NTSB narrative

The pilot was conducting an agricultural flight. Recorded GPS track data showed that as the flight progressed, the airplane made a climbing left turn after each spray pass, the frequency of spray passes increased, the elapsed time between spray passes decreased, and the maximum altitude achieved between spray passes increased. During the final 5 minutes of the flight, the airplane's groundspeed was 160-165 mph during each spray pass and 104-120 mph while in the turn between spray passes; the airplane routinely climbed 450-520 ft after each spray pass. Another agricultural pilot, who was spraying a nearby field at the time of the accident, reported that he maintained radio contact with the accident pilot throughout most of the accident flight and saw the accident airplane consistently climb 450-500 ft after each spray pass. He stated that the climbs between spray passes were higher than required for an aerial-application flight and reported seeing the airplane exit the field in a climb following a spray pass before it rolled right-wing-down into a 90°-100° bank with a 10°-12° nose-up pitch attitude. The airplane then pitched down, consistent with a lazy eight flight maneuver. This pilot lost sight of the accident airplane when he turned his airplane after a spray pass. The airplane's final recorded groundspeed and estimated altitude above ground level were 152 mph and 136 ft, respectively. There were no witnesses to the airplane’s final descent and impact with the ground. The operator’s chief pilot had previously counseled the accident pilot about his “aggressive” flying techniques, including his use of a hammerhead flight maneuver for turns between spray passes. The airplane flight manual (AFM) states that an abrupt pull-up at the end of a spray pass should be avoided to maintain adequate airspeed during the turn between spray passes. The AFM states that a maximum altitude loss of 220 ft is expected during a recovery from a wings-level aerodynamic stall at a gross weight of 8,000 lbs; however, an aerodynamic stall during an uncoordinated turn will result in a sharp decrease in airplane pitch and a significant loss of altitude. The airplane wreckage was found upright in a cornfield with significant impact damage to the forward fuselage and the leading edge of both wings. There were no discernable ground impacts or debris path preceding the wreckage. Postaccident examination revealed no evidence of a preexisting mechanical malfunction or failure that would have precluded normal operation of the airplane. The lack of a wreckage debris path and an estimated 45° nose-down flightpath angle at impact are consistent with an unsuccessful attempted recovery from an aerodynamic stall at a low altitude. The pilot’s postmortem toxicological testing detected ethanol in all tested specimen types. However, the differences between the ethanol levels in the various specimens were greater than is typically seen after ethanol consumption alone and suggest that at least some of the detected ethanol was likely from sources other than ingestion. While it is likely that at least some of the ethanol detected in the pilot’s specimens was from postmortem production, the possibility that the pilot may also have consumed ethanol is not excluded by the toxicology results. However, there is no clear operational evidence that the pilot was impaired. Given the high-risk nature of spraying operations and a pilot known to fly aggressively, positing impairment is not necessary to plausibly explain the accident circumstances. Thus, whether ethanol effects contributed to the accident cannot be determined.

Analysis

Primary failure mode
Human factors
First missed decision gate
Pilot could have adhered to proper turning techniques during spray passes.

NTSB coding

Evidence available

  • ADS-B / radar
  • Photos
  • 17 docket documents
View NTSB final reportView NTSB docket

Docket documents17

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