GULFSTREAM AM CORP COMM DIV 690D near Spokane, WA — 2024-12-02

Probable cause

A partial loss of engine(s) power due ice ingestion.

NTSB narrative

The pilot was conducting a cross-country flight under an instrument flight rules (IFR) flight plan. The pilot set up for a GPS instrument approach and confirmed all deicing equipment was activated before descending into the clouds for landing. During the descent, the airplane encountered moderate rime icing. Upon exiting the cloud layer, the airplane began to descend below the glide path. The pilot advanced the engine throttles, but both engines were unresponsive. He initiated a forced landing to soft terrain short of the runway threshold, which resulted in a hard landing and subsequent landing gear collapse. The airplane sustained substantial damage to the fuselage. Postaccident examination of the airplane showed remnants of moderate rime icing on the right and left wing leading edges. Indications of icing remained visible on the propeller spinner, vertical and horizontal surfaces, and two top fuselage antennas. Severe icing was observed on the stall warning vane, which was likely inoperative as a result. Postaccident examination of the airframe revealed no preaccident mechanical malfunctions or failures that would have precluded normal operation. Control continuity of the power levers and the condition levers for both engines was established from the cockpit controls to both engines. Continuity of the stall warning vane and pitot heat was established from the cockpit switch to the heating elements. Postaccident examination and test runs of both engines revealed no preaccident mechanical failures or malfunctions that would have precluded normal operation. Both engines were operated at various power settings and responded to power lever inputs, including rapid power lever increases. Both engines’ anti-ice valves were activated from the control room and there was audible actuation of the anti-ice valve solenoids. A series of airmen’s meteorological information bulletins (AIRMETs) was active for the area, primarily for IFR and mountain obscuration conditions. The National Weather Service (NWS) Graphic Forecast for Aviation (GFA) flight categories chart for ceilings and visibility current at the time of the accident depicted an extensive area of Low Instrument Flight Rules (LIFR) conditions over the area due to low ceilings and freezing fog. When or if the airplane’s deicing equipment was activated could not be determined based on the available evidence. The ice accumulation visible on the airplane at the accident site suggested that the ice accumulated to such a degree that it likely caused a loss of engine power to both engines due to ice ingestion.

Analysis

Primary failure mode

Environmental

First missed decision gate

Pilot could have aborted the approach due to icing conditions before entering the clouds.

NTSB coding

• Structural icing · Approach-IFR final approach

Evidence available

• ADS-B / radar
• Photos
• 11 docket documents

Docket documents11

• PILOT/OPERATOR AIRCRAFT ACCIDENT REPORT, NTSB FORM 6120.1form
• RELEASE OF AIRCRAFT WRECKAGE, NTSB FORM 6120.15_CUIform
• STATEMENT OF PARTY REPRESENTATIVES TO NTSB INVESTIGATIONinterview
• ENGINE(S) EXAM AND TEST RUNother
• RECORD OF E-MAIL CORRESPONDENCE (FAA)other
• RECORD OF PHONE CONVERSATIONother
• WPR25LA053 - SPOKANE, WA ENVIRONMENTAL FACTORS REVIEWother
• PHOTO ARRAYphotos
• ADS-B FLIGHT TRACKradar
• ADS-B RAW DATAradar
• AIRFRAME AND ENGINE(S) EXAMINATION REPORTreport