Piper PA46 N307JM accident near Mayport, Florida

Probable cause

An in-flight loss of control following an encounter with supercooled large droplet icing conditions, which ultimately resulted in an uncontrolled descent and subsequent inflight breakup. Also causal was the pilot’s failure to maintain an appropriate airspeed for flight in icing conditions.

NTSB analysis

The pilot and his pilot-rated passenger departed under instrument flight rules for a personal cross-country flight and climbed first to 19,000 ft mean sea level (msl), then to 23,000 ft msl several minutes later. Weather and air traffic control radar information indicated that the airplane had been operating in an area of heavy precipitation for about 20 minutes before it entered a descending right turn. A section of the right wing separated as the airplane descended, and the airplane impacted water. Performance calculations revealed that, shortly before the airplane began its descent, its airspeed decreased to between 77 and 90 knots indicated (KIAS). The airplane’s published stall speed at maximum gross weight was 69 KIAS. Because accumulation of ice on the unprotected areas of the airframe increased the airplane’s stall speed, with aerodynamic buffeting occurring up to 19 knots above the normal stall speed, the manufacturer stated that flight in icing conditions should be conducted at a speed not lower than 130 KIAS.

Postaccident examination of the airplane’s flight controls and icing protection system components revealed no evidence of preimpact failure or malfunction. While the filament of the stall warning fail and windshield heat fail warning light bulbs were broken and stretched, potentially consistent with illumination at impact, it could not be determined at what portion of the flight the bulb(s) might have illuminated. Based on the environmental conditions at the time, the stall warning system was likely not accurate or reliable. Although fatigue cracks were noted in the right wing spar web, the cracks did not contribute to the inflight break-up.

The pilot received a preflight weather briefing that included a convective SIGMET outlook and an AIRMET for icing between about 14,000 ft and 27,000 ft msl, valid for the area of the accident site about the time of the accident. Although the pilot did not access specific icing forecasts, which likely understated the potential for icing conditions, there was sufficient information available to the pilot to indicate possible icing at his chosen cruise altitude. The airplane was operating above the freezing level near the top of a mature cumulus cloud formation, which is known to have higher liquid water content, and within a heavy rain shower band. Those conditions likely resulted in an encounter with supercooled large droplet icing conditions, which exceeded the capability of the airplane’s icing protection system.

Given this information, it is likely that the flight encountered icing conditions, which resulted in the airframe accumulating ice in excess of that able to be shed by the airplane’s icing protection system. It is also likely that, because the pilot was operating the airplane below the minimum icing airspeed, it encountered an aerodynamic stall at an airspeed that was higher than normal, which resulted in a loss of control, an uncontrolled descent, and subsequent inflight break-up.

Text from the NTSB. Open the NTSB docket for ERA19LA072 for the full record.