History of Flight
On August 21, 2019, about 1132 Pacific daylight time, a Cessna CE-560XL airplane, registration N91GY, was destroyed when it impacted a ditch and caught fire after overrunning the departure end of runway 2 near Oroville, California. The two pilots and eight passengers were not injured. The flight was a Title 14 Code of Federal Regulations Part 135 on-demand charter.
The pilots reported a normal preflight inspection, passenger boarding, and briefing. They completed before-engine-start and after-start checklists and began taxiing to runway 2. Review of the cockpit voice recorder (CVR) revealed that before engine start, the copilot called out “parking brake” and the pilot replied “set”; the parking brake was not mentioned again during the flight. The crew used a mobile phone to obtain their instrument flight rules clearance during taxi. The CVR showed that most taxi checklist items were not verbalized.
The pilot taxied and stopped short of runway 2 to perform a rudder bias check. He stated that as part of the check he applied the parking brake and kept his feet on the pedals, but the CVR did not capture any verbalization of setting or releasing the parking brake. Airport surveillance video showed the airplane holding short of runway 2 for about 3 minutes 44 seconds.
About 1 minute 30 seconds before takeoff, the CVR captured discussion of a NO TAKEOFF annunciator for an unsafe trim setting and that the autopilot had engaged due to a shifting tablet. The pilots reset the trim, and the autopilot was disconnected. About 30 seconds before takeoff thrust, a turn knob annunciator illuminated; the copilot asked if they should continue, and the pilot said they would go and not turn on the autopilot until they figured it out.
Engine RPM increased about 7 seconds later, and takeoff power was confirmed 8 seconds after that. About 2 seconds later, the copilot said the airplane was barely moving and that something was not right. The pilot stated the airplane was rolling and asked for speed callouts. About 16 seconds later, the pilot noted more runway usage than expected. The copilot called out takeoff-decision speed, then rotation speed. The pilot rotated but the airplane did not lift off. He pulled the yoke back again “harder” to his chest with no nose movement. Shortly after, the pilot applied full thrust reversers and maximum braking. The airplane exited the runway frame about 730 feet beyond the runway 20 threshold, overran the departure end, impacted a ditch, lost its landing gear, skidded across grass, and a postcrash fire ensued.
Aircraft Information
The Cessna CE-560XL (N91GY) was equipped with a parking brake that employed controllable check valves to trap hydraulic fluid. The parking brake was set by depressing the toe brakes and pulling a black knob on the lower left instrument panel. The force applied to the toe brakes before pulling the knob determined the brake pressure. The manufacturer’s manual did not specify required force or duration. The parking brake could trap pressure even if the knob was pulled before toe brake application, but this was not in the manual. The parking brake knob was obscured from the right seat.
During postaccident interviews, the pilot said he normally pressed the toe brakes enough to stop, then “a little bit more,” and pulled the lever. He believed that if the parking brake was set, the airplane should not move with takeoff power applied. The copilot said he had no expectations. The head of training for the pilots’ training center stated that no CE-560XL manual, checklist, or curriculum contained a caution that takeoff speeds could be achieved with partial parking brake pressure.
The airplane had a NO TAKEOFF warning light that illuminated for conditions such as flaps not in takeoff range, elevator out of trim, horizontal stabilizer out of takeoff position, or speed brakes out of position; the parking brake was not part of these conditions.
Checklists from the operator (Delta Private Jets) and manufacturer required the parking brake to be set before engine start, with no further parking brake items until shutdown. The taxi checklist included “brakes…check,” which the manufacturer stated was a brake test, and the operator’s flow diagram referred to toe brakes. The rudder bias check was a checklist item; the pilot stated he normally verbalized “parking brake on, parking brake off” during that check, but did not do so because the copilot was on the phone.
The parking brake certification standard (14 CFR 25.735, originally 1965) required the parking brake to prevent rolling on a paved level runway with takeoff power on the critical engine. The CE-560XL was certified in 1998 to that standard. The manufacturer demonstrated that the brake prevented roll when set with full pressure and one engine at takeoff power. It was not tested with both engines. An amendment effective May 2002 required cockpit indication when the parking brake was not fully released, but the CE-560XL, certified in 1998, was not required to have such indication.
Wreckage and Impact
The airplane came to rest about 1,990 feet beyond the departure end of runway 2, on a heading of about 078°. Tire transfer marks originated near the hold short line and extended the full length of the runway, overrun, and into grass. All major structural components were found near the main wreckage. The postcrash fire consumed much of the airframe, including the cockpit. The right wing was ruptured and fire-damaged; the left wing was mostly intact outboard of the root. The empennage was intact. The parking brake cable and handle were found with the handle in a position consistent with OFF, but the brake valve (damaged by fire) had its lever in the ON position. Computed tomography confirmed the valve internals were closed, consistent with ON.
Performance Information
Data from the flight data recorder (FDR) showed that 16 of 59 parameters contained invalid data, including airspeed. Analysis of longitudinal acceleration data revealed a maximum speed of about 120 knots during the takeoff sequence. Calculated takeoff-decision and rotation speeds for a normal configuration were 106 knots; angle-of-climb speed was 123 knots.
A performance study using FDR, CVR, ADS-B, airport video, tire marks, and the flight manual indicated the airplane could have accelerated to rotation speed and safely taken off with normal configuration. However, the study found that the airplane’s performance was substantially degraded by an unexpected retarding force at the wheel/runway interface. This force adversely affected acceleration, rotation capability, and deceleration. Pitching moment calculations showed that the retarding force produced a nose-down moment that matched or exceeded the available nose-up elevator authority at rotation speed for the accident center of gravity, preventing rotation.