Cessna 560XL

Full Narrative

HISTORY OF FLIGHTOn August 21, 2019, about 1132 Pacific daylight time, a Cessna CE-560XL airplane, N91GY, was destroyed when it was involved in an accident near Oroville, California. The two pilots and eight passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 135 on-demand charter flight. 

The pilot and copilot reported that, after a normal preflight inspection was completed, the passengers boarded the airplane, and the pilot briefed the passengers. Both the pilot and copilot conducted the before engine start checklist through the after-start checklist and began taxiing to runway 2. Review of the cockpit voice recorder (CVR) recording revealed that, before engine start, the copilot called out “parking brake” and the pilot replied, “set”; the crew did not otherwise mention the parking brake. According to the pilot, the pilot and copilot completed most of the items on the taxi checklist during the taxi before the airplane neared runway 2, then the copilot used a mobile phone to call the Federal Aviation Administration Air Route Air Traffic Control Center and obtain their instrument flight rules departure clearance and release. Review of the CVR recording reveals that the pilot and copilot did not verbalize most of the items on the taxi checklist.

The pilot reported that he continued to taxi and stopped short of runway 2, where he performed a rudder bias check. The pilot stated that, as part of the rudder bias check, he applied the parking brake then kept his feet on the pedals to feel the rudder pedal movement. Review of the CVR recording confirmed that the pilot did not verbalize the rudder bias check or setting or releasing the parking brake as part of the rudder bias check. The pilot reported that, after obtaining their instrument flight rules clearance, the flight crew updated the flight management system. Review of airport surveillance video showed the airplane holding short of runway 2 for about 3 minutes 44 seconds.

Review of the CVR recording revealed that, about 1 minute 30 seconds before takeoff, the pilot and copilot discussed that a NO TAKEOFF annunciator had illuminated in the cockpit for an unsafe trim setting and that the autopilot had engaged. The CVR captured a sound consistent with the autopilot being disconnected, then the flight crew discussed that a tablet had accidentally shifted and engaged the autopilot. The pilots then discussed resetting the trim, which the copilot corrected.

About 30 seconds before the application of takeoff thrust, the pilot and copilot discussed a turn knob annunciator that had illuminated in the cockpit. The copilot discussed that he did not know the meaning of the message and asked whether the pilot wanted to continue with the flight. The pilot responded they would go and would not turn the autopilot on until they figured it out.

The airplane’s engine RPM increased about 7 seconds later, followed by the confirmation of takeoff power set by the copilot 8 seconds after that. About 2 seconds after the copilot confirmed takeoff power set, he said that the airplane was barely moving then stated that something was not right. About 3 seconds later, the pilot stated the airplane was rolling and told the copilot to call speeds, which the copilot acknowledged. About 16 seconds later, the pilot indicated that the airplane was using more runway than he expected. The copilot called out the takeoff-decision speed 2 seconds later and said “rotate” for rotation speed 1 second after that. The pilot then said “rotate.”

The pilot stated in a postaccident interview that “it was just a weird sensation” as he pulled the yoke back and the airplane didn’t lift off, and he noticed no movement of the nose when pulling the yoke back a second time “harder” to his chest. Shortly after, the pilot applied full thrust reversers and maximum braking. A sound consistent with thrust reverser application was captured on the CVR recording about 1 second after the airplane had exited the frame of the airport surveillance camera. The position at which the airplane moved out of the surveillance camera frame was about 730 ft beyond the runway 20 threshold. The airplane exited the departure end of the runway and impacted a ditch. The landing gear separated from the airplane during the accident sequence, and the airplane skidded to a stop across a grass-covered area, and a postcrash fire ensued.
PERSONNEL INFORMATIONThe pilot, who was the pilot flying during the accident flight, held a pilot-in-command type rating for the CE-560XL, CE-525S airplanes. The pilot’s most recent proficiency check about 3 months before the accident flight was his initial type rating for the accident make and model.

The copilot was the pilot monitoring for the accident flight and qualified as captain by the operator. He held a pilot-in-command type ratings in the CE-560XL, CE-750, and second-in-command privileges for the ERJ-170/190. About a month before the accident flight, the copilot completed his most recent simulator training, which included recurrent training for the CE-560XL.
AIRCRAFT INFORMATIONParking Brake

According to the manufacturer’s operating manual, the accident airplane’s parking brake was part of the CE-560XL’s “normal brake system” and employed “controllable check valves that could prevent the return of hydraulic fluid after the brakes have been set.” The left-seat pilot normally sets the parking brake by “depressing the toe brakes and pulling out the black parking brake handle [pull knob] located on the lower left side of the instrument panel” (see exemplar CE-560XL in figure 1). The parking brake’s power (or resistance) could vary and is dependent upon the amount of force the pilot applied to the toe brakes before pulling the parking brake pull knob. The manufacturer’s operating manual does not specify how much force or length of time to apply to the toe brakes while setting the parking brake.

If the CE-560XL toe brakes are not fully depressed when the parking brake valve is engaged, then only partial pressure would be trapped by the parking brake valve. In a submission for this investigation, the manufacturer stated that the parking brake valve is designed to also trap pressure in the brake lines if the parking brake pull knob is pulled first, followed by application of the toe brakes, but the manufacturer’s operating manual does not include that information. The parking brake pull knob on the CE-560XL is located on the lower left side of the instrument panel near the left-seat pilot’s left knee, which obscures it from the view of the right-seat pilot (see figure 2).


Figure 1: View of the parking brake pull knob in the ON position in reference to the instrument panel in an exemplar CE-560XL.

Figure 2: Location of the obscured parking brake pull knob within an exemplar CE-560XL

When asked how to normally engage the parking brake during a postaccident interview, the pilot stated that he normally pressed on the toe brakes enough to stop the airplane’s taxi movement then pushed the toe brakes “a little bit more” and pulled the “lever.” He added that “you’re not standing on [the toe brakes].” The pilot further reported that it was his understanding that if the parking brake was set on the CE-560XL, the airplane “shouldn’t move” with takeoff power applied. When the copilot was asked if he believed the airplane could move with the parking brake engaged, he reported, “I have no expectations for anything.” According to the head of training at the training center where the pilot and copilot received their CE-560XL training, no CE-560XL airplane flight manual, checklist, or training curriculum provided a caution or warning that takeoff speeds may be achievable with full or partial pressure applied to the parking brake.

Takeoff Warning Annunciator

The airplane was equipped with a NO TAKEOFF warning light as part of the annunciator panel, but the parking brake lever was not a part of the alerting conditions. The airplane operating manual stated, in part:

On the ground, the amber no takeoff annunciator will illuminate steadily if one or more of the following conditions exist: Flaps not within takeoff range (less than 7° or more than 15°), elevator out of trim for takeoff, horizontal stabilizer is out of takeoff position, or speed brakes are out of takeoff position. … Pressing the master caution will cause the flashing annunciator to change to steady on and the master caution to extinguish.

Checklists

Delta Private Jets (the operator) produced its normal CE-560XL checklists, which were adapted from the manufacturer’s airplane flight manual checklists, and the operator required its pilots to use the operator’s checklists. The Federal Aviation Administration certificate managing office accepted these adapted operator checklists in May 2017. The manufacturer’s “before starting engines” checklist called for the “park brake” to be set and the operator’s “before start” checklist called for the parking brake to be set by the left-seat pilot; therefore, both the manufacturers and operator’s checklists call for the parking brake to be set before the engines are started. There were no further checklist items referring to the parking brake in the manufacturers and operator’s checklists until the shutdown checklist.

The third item of manufacturer’s taxi checklists stated, in part, “brakes…check”; the manufacturer stated that this step calls for the brakes to be tested. The operator’s taxi checklist also includes this item, but its flow diagram in the standard operating procedures points to the toe brakes rather than the parking brake pull knob for this checklist item.

The rudder bias system is a check item in the operator’s taxi checklist and the manufacturers before taxi checklist. The operator’s rudder bias check procedures direct the pilot flying to verbalize “left throttle, left rudder… right throttle, right rudder” while checking the rudder bias. The pilot stated that he typically would have verbalized “parking brake on, parking brake off” when performing the rudder bias check; however, because the copilot was on the phone obtaining clearance and release for the flight, he did not verbalize those callouts during taxi.

Certification

The parking brake standard outlined in 14 CFR 25.735, Brakes and Braking Systems, was first established in 1965 and remained the standard until May 2002. To meet the original requirements of 14 CFR 25.735 in force between 1965 and 2002, the parking brake must prevent the airplane from rolling on a paved, level runway when set by the pilot with takeoff power on the critical engine. To certify the CE-560XL parking brake to that standard, the manufacturer demonstrated that the parking brake prevented the airplane from rolling when set with full parking brake pressure applied and one engine at takeoff power. The parking brake was not required to be tested with both engines at takeoff power, and the manufacturer did not test this condition.

Effective May 2002, the Federal Aviation Administration amended 14 CFR 25.735 (Amendment 25-107) to state, in part, “There must be indication in the cockpit when the parking brake is not fully released.” However, the CE-560XL was initially certificated in 1998 (4 years before the parking brake indication amendment) and built to the initial 1965 standard, which does not require a cockpit indication if the parking brake is not fully released.
AIRPORT INFORMATIONParking Brake

According to the manufacturer’s operating manual, the accident airplane’s parking brake was part of the CE-560XL’s “normal brake system” and employed “controllable check valves that could prevent the return of hydraulic fluid after the brakes have been set.” The left-seat pilot normally sets the parking brake by “depressing the toe brakes and pulling out the black parking brake handle [pull knob] located on the lower left side of the instrument panel” (see exemplar CE-560XL in figure 1). The parking brake’s power (or resistance) could vary and is dependent upon the amount of force the pilot applied to the toe brakes before pulling the parking brake pull knob. The manufacturer’s operating manual does not specify how much force or length of time to apply to the toe brakes while setting the parking brake.

If the CE-560XL toe brakes are not fully depressed when the parking brake valve is engaged, then only partial pressure would be trapped by the parking brake valve. In a submission for this investigation, the manufacturer stated that the parking brake valve is designed to also trap pressure in the brake lines if the parking brake pull knob is pulled first, followed by application of the toe brakes, but the manufacturer’s operating manual does not include that information. The parking brake pull knob on the CE-560XL is located on the lower left side of the instrument panel near the left-seat pilot’s left knee, which obscures it from the view of the right-seat pilot (see figure 2).


Figure 1: View of the parking brake pull knob in the ON position in reference to the instrument panel in an exemplar CE-560XL.

Figure 2: Location of the obscured parking brake pull knob within an exemplar CE-560XL

When asked how to normally engage the parking brake during a postaccident interview, the pilot stated that he normally pressed on the toe brakes enough to stop the airplane’s taxi movement then pushed the toe brakes “a little bit more” and pulled the “lever.” He added that “you’re not standing on [the toe brakes].” The pilot further reported that it was his understanding that if the parking brake was set on the CE-560XL, the airplane “shouldn’t move” with takeoff power applied. When the copilot was asked if he believed the airplane could move with the parking brake engaged, he reported, “I have no expectations for anything.” According to the head of training at the training center where the pilot and copilot received their CE-560XL training, no CE-560XL airplane flight manual, checklist, or training curriculum provided a caution or warning that takeoff speeds may be achievable with full or partial pressure applied to the parking brake.

Takeoff Warning Annunciator

The airplane was equipped with a NO TAKEOFF warning light as part of the annunciator panel, but the parking brake lever was not a part of the alerting conditions. The airplane operating manual stated, in part:

On the ground, the amber no takeoff annunciator will illuminate steadily if one or more of the following conditions exist: Flaps not within takeoff range (less than 7° or more than 15°), elevator out of trim for takeoff, horizontal stabilizer is out of takeoff position, or speed brakes are out of takeoff position. … Pressing the master caution will cause the flashing annunciator to change to steady on and the master caution to extinguish.

Checklists

Delta Private Jets (the operator) produced its normal CE-560XL checklists, which were adapted from the manufacturer’s airplane flight manual checklists, and the operator required its pilots to use the operator’s checklists. The Federal Aviation Administration certificate managing office accepted these adapted operator checklists in May 2017. The manufacturer’s “before starting engines” checklist called for the “park brake” to be set and the operator’s “before start” checklist called for the parking brake to be set by the left-seat pilot; therefore, both the manufacturers and operator’s checklists call for the parking brake to be set before the engines are started. There were no further checklist items referring to the parking brake in the manufacturers and operator’s checklists until the shutdown checklist.

The third item of manufacturer’s taxi checklists stated, in part, “brakes…check”; the manufacturer stated that this step calls for the brakes to be tested. The operator’s taxi checklist also includes this item, but its flow diagram in the standard operating procedures points to the toe brakes rather than the parking brake pull knob for this checklist item.

The rudder bias system is a check item in the operator’s taxi checklist and the manufacturers before taxi checklist. The operator’s rudder bias check procedures direct the pilot flying to verbalize “left throttle, left rudder… right throttle, right rudder” while checking the rudder bias. The pilot stated that he typically would have verbalized “parking brake on, parking brake off” when performing the rudder bias check; however, because the copilot was on the phone obtaining clearance and release for the flight, he did not verbalize those callouts during taxi.

Certification

The parking brake standard outlined in 14 CFR 25.735, Brakes and Braking Systems, was first established in 1965 and remained the standard until May 2002. To meet the original requirements of 14 CFR 25.735 in force between 1965 and 2002, the parking brake must prevent the airplane from rolling on a paved, level runway when set by the pilot with takeoff power on the critical engine. To certify the CE-560XL parking brake to that standard, the manufacturer demonstrated that the parking brake prevented the airplane from rolling when set with full parking brake pressure applied and one engine at takeoff power. The parking brake was not required to be tested with both engines at takeoff power, and the manufacturer did not test this condition.

Effective May 2002, the Federal Aviation Administration amended 14 CFR 25.735 (Amendment 25-107) to state, in part, “There must be indication in the cockpit when the parking brake is not fully released.” However, the CE-560XL was initially certificated in 1998 (4 years before the parking brake indication amendment) and built to the initial 1965 standard, which does not require a cockpit indication if the parking brake is not fully released.
WRECKAGE AND IMPACT INFORMATIONExamination of the accident site revealed that the airplane came to rest about 1,990 ft beyond the departure end of runway 2 on a heading of about 078°.

Examination of the runway revealed tire transfer marks which originated from near the runway 2 hold short line and progressed onto the runway then continued throughout the entire length of the runway, runway overrun, and a perpendicular oriented runway (see figure 3). The tire marks extended into a grassy area, across a taxiway, and within the grassy area near the main wreckage (see figure 4).


Figure 3: View of the approach end of runway 2, with right main landing gear (MLG) transfer marks annotated.


Figure 4: View of the accident site and runway environment.

All major structural components of the airplane were located within the vicinity of the main wreckage.

Examination of the wreckage revealed that the postcrash fire consumed a majority of the airframe. The right wing was ruptured open and extensively fire damaged. The left wing was mostly intact just outboard of the wing root. The empennage (rudder, vertical, horizontal, and elevators) was intact and unremarkable. The cockpit area was heavily damaged by the postcrash fire.

The parking brake cable and handle were located in the wreckage, but the parking brake plastic knob was not present. The cockpit end of the parking brake cable and handle was found in a position consistent with the OFF position. The cable was continuous from the handle to the parking brake valve.

The parking brake valve was located loose in the wreckage and was damaged by fire. The parking brake control cable was attached to the valve and all attaching hardware was present. The cable was removed from the valve without disturbing the valve lever position, but the cable could not be actuated due to unknown obstructions/interference that could not be determined on scene. Based on a visual inspection of the lever position, the brake valve was in the ON position, as shown in figure 5. No part identification or data plate could be found on the component.


Figure 5: Parking brake valve after removal from the wreckage

The parking brake valve was scanned using computed tomography and the resulting images showed internal valve components in a closed position, which is consistent with an ON position.
ADDITIONAL INFORMATIONData obtained from the onboard flight data recorder revealed that 16 of the 59 parameters, including airspeed, contained invalid data. A performance study based upon longitudinal acceleration data (which was found to be valid) revealed that the airplane had reached a maximum speed of about 120 knots during the takeoff sequence, as shown in figure 6. The calculated takeoff-decision and rotational speeds in a normal configuration for the accident takeoff were 106 knots, and angle-of-climb speed was calculated to be 123 knots.


Figure 6: Comparison of calculated ground speed, flight data recorder airspeed, and automatic dependent surveillance-broadcast data.
The aircraft performance study, which used information from the flight data recorder, CVR, automatic dependent surveillance-broadcast, airport surveillance camera, tire witness marks, and the airplane flight manual, indicated that the accident airplane was able to accelerate to the rotation speed required for the airplane to lift off and had adequate takeoff performance capability to safely take off from runway 2 when configured for a normal takeoff. However, the information from the above sources and engineering models used to calculate the lift, drag, and engine thrust components during the accident takeoff roll, indicated that the airplane’s performance was substantially degraded by an unexpected retarding force acting at the wheel/runway interface.

Using the CE-560XL weight and balance envelope and the accident airplane’s full-forward center of gravity (CG) position when loaded at the aft limit, the airplane nose up CG pitching moment capability was calculated between about 10,300 and 12,800 ft-pounds (ft-lb). Based on CE-560XL engineering drawings and the accident airplane’s weights, a vertical moment arm was estimated at 3.5 ft. The airplane nose down pitching moment calculations using CE-560XL engineering models (figure 7) indicate about 13,000 ft-lb for groundspeeds between 90 and 110 knots and a 3.5 ft moment arm, which matches or exceeds the available airplane nose up pitching moment capability for the accident CG loading values. Thus, the accident airplane’s unexpected retarding force directly competed against and could inhibit airplane nose up elevator/horizontal stabilizer authority at rotation speed for the accident CG loading value.



Figure 7: Estimated airplane nose down pitching moment due to calculated equivalent retarding force during the accident takeoff ground roll.

The magnitude and direction of the unexpected retarding force adversely affected the airplane’s acceleration and rotation capability during the attempted takeoff as well as deceleration capability when stopping. Figure 8 shows the airplane’s groundspeed for previous takeoff sequences as compared to its degraded groundspeed during the accident takeoff (black line and symbols).


Figure 8: Calculated airplane groundspeed values for previous takeoffs and the accident takeoff.