Summary
On the morning of the accident, an EMB-500 airplane operating under 14 CFR Part 91 on an instrument flight rules flight plan crashed while on approach to runway 14 at Montgomery County Airpark (GAI) in Gaithersburg, Maryland. The airplane struck three houses and the ground approximately 3/4 mile from the approach end of the runway. A postcrash fire involved the airplane and one of the houses, which contained three occupants. The pilot, two passengers, and the three people in the house died as a result of the accident. The airplane was destroyed by impact forces and the postcrash fire. Visual meteorological conditions prevailed at the time of the accident.
Flight Data
Data from the airplane’s cockpit voice and data recorder (CVDR) indicated that the flight departed from Horace Williams Airport in Chapel Hill, North Carolina, at about 0945. The takeoff and cruise portions were uneventful. Approximately 15 minutes after takeoff, the passenger in the right cockpit seat stated that the airplane was “in the clouds.” Seconds later, the airplane’s engine anti-ice system and the wing and horizontal stabilizer deice system were manually activated for about 2 minutes before being manually turned off. About 6 minutes after that, the automated weather observing system (AWOS) at GAI began transmitting over the pilot’s audio channel, providing information that conditions were conducive to icing during the approach. The CVDR recorded no further activity or faults for either ice protection system, indicating the pilot did not turn the systems back on.
Before the airplane descended through 10,000 ft, the pilot was expected to perform the Descent checklist from the Quick Reference Handbook (QRH). Based on the AWOS-reported weather conditions, the Normal Icing Conditions checklist required turning on the engine anti-ice and wing and horizontal stabilizer deice systems, and using landing distance performance data accounting for deice activation. However, CVDR data show that before descent, the pilot set the landing reference speed (Vref) at 92 knots, indicating use of performance data for operation with the deice system off and an airplane landing weight less than actual. The appropriate checklist and accurate weight would have required an approach speed of 126 knots (Vref 121 knots +5 knots).
Probable Cause
The National Transportation Safety Board determined that the probable cause of this accident was the pilot’s conduct of an approach in structural icing conditions without turning on the airplane’s wing and horizontal stabilizer deice system, leading to ice accumulation on those surfaces, and without using the appropriate landing performance speeds for the weather conditions and airplane weight, as indicated in the airplane’s standard operating procedures, which together resulted in an aerodynamic stall at an altitude at which a recovery was not possible.