Challenger 300 pitch upset near Windsor Locks, 2023

What happened

1. 1526

   Takeoff roll on runway 2 at Keene, at 1526:11. The right pitot probe cover is still on. About 16 seconds later the crew reject the takeoff at a maximum of 104 kt on the left PFD. The second in command (SIC) said the right airspeed never showed more than 40 kt. He finds the cover and removes it.

2. After the rejected takeoff the cyan advisory RUDDER LIMITER FAULT is displayed. It is a No-Go item with no MEL relief. The crew do not check the Go/No-Go guide. The SIC asks whether the pilot in command (PIC) wants to take off with it. The PIC calls it advisory only.

3. 1535

   Airborne from runway 2 at 1535:27. MACH TRIM FAIL comes up at about 400 ft. AP STAB TRIM FAIL appears as soon as the autopilot is engaged.

4. 1536

   At 1536:52 the autopilot disconnects. The PIC says "I did that." He re-engages it two more times in the climb and does not announce the changes. At 1537:58 the SIC says he would leave the autopilot off and the PIC agrees. The last engagement, at 6,230 ft, stays in until 22,780 ft.

5. In the climb the PIC asks for "the checklist" without naming one. About 8 minutes later the SIC picks PRI STAB TRIM FAIL from the quick reference card. No fault on the airplane could produce that message.

6. 1544

   At 1544:08 the SIC says "stab trim off" as he moves the STAB TRIM switch from PRI to OFF, the checklist's first step. The autopilot disconnects at about 23,000 ft. It had been holding 5.3° of nose-down elevator.

7. In the next seconds, pitch goes from 3° to 11° nose up in one second and normal acceleration rises to 4 g. The PIC pushes with at least 90 lb and load drops to -2.3 g. Then the column comes back and the nose goes past 20° up with more than 4 g. The flight data recorder stops when its g switch trips. The flaps-up limit is +2.6 g.

8. A passenger finds the passenger from seat 3 lying in the aisle near the lavatory. The crew tell ATC about the medical emergency and divert. They land at Bradley International about 17 minutes after the upset.

All times are local, from the flight data recorder and the NTSB report.

Why it happened

1. The NTSB found the probable cause to be the crew's failure to remove the right pitot probe cover before flight, their decision to depart with a No-Go advisory after the rejected takeoff, and their choice of the wrong non-normal checklist in flight. Together these led to an upset beyond the airplane's manoeuvring load limits that fatally injured an unbelted passenger. The report found that the PIC's decision to continue the climb and use the autopilot while troubleshooting, and his pilot-induced oscillations after the autopilot let go out of trim, added to the severity. Inadequate crew resource management also contributed.¹

2. The SIC was interrupted by a lineman delivering ice during the preflight and left the cover on the right probe. The PIC did not notice it.¹

3. The SIC had questioned the departure, the autopilot use and the continued climb. The PIC went ahead as planned.¹

4. The AP STAB TRIM FAIL or AP HOLDING NOSE DOWN checklists would likely have prevented the accident. Both warn of an out-of-trim condition and a sudden force change at autopilot disconnect. They tell the crew to hold the controls firmly and keep speed and configuration changes small. A temporary revision to AP STAB TRIM FAIL, TR-39-1 of 15 June 2022, was in both the electronic and paper QRH.¹

5. The operator's director of operations said maintenance control would likely have had the crew shut down and restart, which would likely have cleared the latched faults.¹

The report makes no safety recommendations.¹

What a crew can take from it

1. An interrupted walkaround can miss an item. The SIC was stopped mid-check by an ice delivery and resumed where he thought he had stopped. The cover stayed on, and the PIC did not see it either. The operator's manual called for a final walk-around by the PIC before the door was closed on each leg.

2. A message after a rejected takeoff is a dispatch question. RUDDER LIMITER FAULT was a No-Go item, and it came from faults the rejected takeoff had latched. The crew did not check the Go/No-Go guide or call maintenance control. The NTSB says maintenance control would likely have had them power the airplane down, which would likely have cleared the faults.

3. Run the checklist that matches the message on the screen. The crew had MACH TRIM FAIL, AP STAB TRIM FAIL and AP HOLDING NOSE DOWN. They ran PRI STAB TRIM FAIL, which no fault on the airplane could produce. The NTSB found that the autopilot messages came and went as the PIC disconnected and re-engaged it, which likely made the choice harder.

4. Expect a jolt when the autopilot lets go out of trim. The autopilot was holding 5.3° of nose-down elevator. When it dropped out, pitch oscillations followed, past 4 g against a +2.6 g limit. The correct checklists warned of a sudden change in control force and called for holding the controls firmly.

5. Get the cabin seated before a step that can upset the airplane. The sign was on for the whole flight, so the passengers had to judge for themselves when to move about. The NTSB says the correct checklist would have warned the crew in time to make sure everyone was seated and belted.

Study it on the course

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Sources

1. National Transportation Safety Board. Aviation Investigation Final Report ERA23LA135, Bombardier BD-100-1A10, N300ER, Windsor Locks, Connecticut, 3 March 2023. Published 5 December 2024.
2. NTSB, public docket ERA23LA135 (32 items, including the flight data recorder and flight test factual reports).
3. NTSB, Flight Testing Factual Report, ERA23LA135.
4. Aviation Safety Network, occurrence 308883.
5. AIN, NTSB: Crew Errors Led to Fatal Injury Onboard Challenger, 6 December 2024.