NTSB probes trim settings and spatial disorientation in fatal Learjet 55 crash near Philadelphia

A fatal crash involving a medical Learjet 55 near Northeast Philadelphia airport on 31 January 2025 remains under investigation as officials probe the influence of trim settings and spatial disorientation on the accident. The jet crashed at high speed only about one minute after departure, killing all six occupants onboard along with one person on the ground. With no flight data recorder onboard and an unusable cockpit voice recorder, investigators face challenges piecing together what exactly unfolded during the flight's critical moments.

The absence of comprehensive flight recorder data has complicated efforts by the National Transportation Safety Board (NTSB) to determine the crash’s cause. Earlier hopes that the ground proximity warning system would yield valuable information ended after damage to that unit and limitations on data content forced investigators to abandon this avenue. The NTSB has yet to issue any cause findings for the accident as it continues its detailed examination.

Focus has shifted in part to the aircraft’s pitch-trim settings during takeoff. From recovered weight and balance data and a checklist found among the debris, experts believe the recommended takeoff pitch trim setting should have been 5.5°. However, inspection of the wreckage’s pitch-trim actuator suggested a trim position equivalent to 3.97°. The condition of the jackscrew mechanism showed no signs of mechanical issues or runaway trim.

Since actual trim positions were not recorded electronically, the inquiry struggles to ascertain whether the aircraft’s trim was set correctly before takeoff or adjusted during flight. Bombardier, the aircraft manufacturer, conducted trajectory-based simulations that calculated pilot control forces for different assumed trim settings. For example, if the pilot had used the 5.5° trim throughout, calculations suggest initial back-pressure on the controls transitioning to increasing push forces as the flight progressed. The 3.97° assumption corresponded to a more pronounced nose-down trim posture.

The trim angle’s relevance is underscored by the aircraft’s sudden and unexplained descent after reaching a peak altitude near 1,320 feet above ground level. This transition happened roughly thirty seconds after the jet entered an overcast cloud layer at about 400 feet during nighttime conditions. At cloud entry, the aircraft was climbing at about 2,300 feet per minute at 191 knots, but the climb rate diminished rapidly and then changed to an accelerating descent, peaking at a fall rate near 10,000 feet per minute.

No evidence was found indicating a decrease in engine thrust during the flight, ruling out power loss as a factor in the descent. The loss of external visual references in night and cloud conditions raises the possibility that spatial disorientation affected the crew. Such conditions can induce somatogravic illusions, confusing the vestibular system and impairing pilot perception of aircraft pitch and acceleration.

The NTSB has not concluded whether spatial disorientation played a role or if it influenced pilot inputs including posture on the control column or trim adjustments. The investigation is incorporating various data, including evaluations of medical equipment found onboard such as oxygen supply, analysis of operator training and risk assessments, and interviews with training staff to provide a fuller picture of potential operational factors.

These comprehensive review efforts by the NTSB reflect the complexity and remaining uncertainties surrounding this particular accident. The final report will depend heavily on forensic analysis in the absence of direct flight data, focusing on engineering inspections, pilot physiology, crew actions, and environmental conditions as intertwined contributors.