ASN Wikibase Occurrence # 311656
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| Date: | Sunday 6 December 2020 |
| Time: | 21:10 LT |
| Type: |  Piper M600 SLS |
| Owner/operator: | |
| Registration: | N282ST |
| MSN: | 4698111 |
| Year of manufacture: | 2019 |
| Total airframe hrs: | 91 hours |
| Engine model: | Pratt & Whitney PT6A-42A |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | Leesburg, Virginia -
 United States of America
|
| Phase: | Landing |
| Nature: | Private |
| Departure airport: | Stuart-Witham Field, FL (SUA/KSUA) |
| Leesburg, VA | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot reported that, after touchdown, while rolling straight down the runway, the airplane 'went careening to the left.â He stated that the right brake locked, and the right main landing gear (MLG) tire 'blewâ as the airplane skidded. The pilot applied rudder and brake inputs to correct the deviation and was able to straighten the airplane's path; however, the airplane exited the left side of the runway and came to rest in the grass. The calculated crosswind component at the time of landing was 7 kts with gusts to 12 kts.
Examination of the runway revealed distinct tire marks from the nose landing gear (NLG) and both MLG extending from the touchdown point on the runway to where the airplane exited the left side of the runway. The NLG tire mark was a dark, wide line with no evident tread pattern, consistent with the airplane skidding from the touchdown point to the runway departure point.
The left MLG tire marks displayed an evident tread pattern consistent with tires rolling under the application of brakes for the entire length. The right MLG tire marks had an evident tread pattern, consistent the tires rolling while braking was being applied, that then changed to a dark wide mark consistent with a skidding tire. The rubber transfer marks then changed to a light mark, likely as a result of the right MLG tire deflating due to wear through the tread.
Examination of the NLG revealed that the tire's right sidewall exhibited crosswise scuffing and the NLG fork was bent left about 10° left. A review of avionics data revealed that the airplane experienced an initial slight lateral acceleration to the right after the MLG touched down, followed by a more significant left lateral acceleration when the NLG touched down about 2 seconds later. The heading began to diverge left of the track when the NLG touched down. About 5 seconds after touchdown, the heading and lateral acceleration transitioned to the right, even though the airplane was still tracking to the left side of the runway. All of these factors are consistent with the NLG tire having been turned to the left at the time of touchdown and with the tire then skidding throughout the landing roll.
Examination of the steering horn revealed that some dimensions exceeded specified tolerances, but they were slight and would have a negligible effect on the function of the steering. Examination of the steering system did not reveal any anomalies or malfunctions that would have precluded normal operation. Following the incident, the NLG tire pressure was measured at 33 psi, significantly lower than manufacturer recommendations.
Given the significant crosswind component at the time of the landing, it is likely that the pilot was correcting for this crosswind component with left rudder input and did not neutralize the rudder pedals, and the NLG wheel, before NLG touchdown.
Other Incidents
N641WA
The airplane departed the left side of the runway shortly after touchdown and came to rest in the dirt and grass adjacent to the runway after the NLG collapsed. The wind at the time of the incident was variable at 3 kts. The pilot checked the NLG tire pressure and added air 2 days before the event. The NLG tire pressure was 78 psi when measured 3 days after the event and decreased to 64 psi 8 days after the event. It is likely that the NLG tire pressure was below recommended at the time of the incident. Data from the airplane showed two distinct oscillations in lateral acceleration after NLG touchdown before the excursion to the left. The heading and track diverged during the excursion, with the heading reaching a maximum of 60º left of the track. The skid marks show the airplane in a left skid with all three tires skidding. The airplane had the new configuration steering horn installed at the time of the incident which had some dimensions out of tolerance. Examination of the steering horn did not reveal any anomalies that would have precluded normal operation. The available information suggests that the pilot over-controlled the airplane in response to the initial lateral acceleration experienced upon NLG touchdown. The low tire pressure likely contributed to the event.
N831PS
The pilot experienced a veer to the left during landing on runway 33, but was able to control the airplane before it departed the runway surface. The wind at the time of the incident was from 120º at 3 kts. The pilot examined the airplane after the event and finding no damage, returned to his home airport. The NLG tire pressure after this flight was 72 psi. Examination of the steering horn did not reveal any anomalies that would have precluded normal operation. The data showed a deviation to the left with a response to the right as reported by the pilot. The available evidence suggests that the low tire pressure contributed to the left veer.
N115NX
The first of this airplane's three steering events occurred in December 2019 during a delivery flight performed by a manufacturer test pilot. The airplane departed the right side of runway 18 after touching down and came to rest on a taxiway. The wind at the time of the incident was from 190º at 9 kts. All tire pressures measured about 10 psi low and the steering horn pads-to-roller dimensions were significantly out of tolerance. The steering horn was replaced with a new unit but of the older configuration. The available information suggests that the tire pressure and play in the steering system contributed to the excursion.
The second event occurred in June 2020 after the airplane had been purchased. During landing on runway 22, the airplane veered to the right upon NLG touchdown, but did not leave the runway surface. The wind at the time of the incident was from 210º at 11 kts. The pilot reported that he had very little time in the PA-46-600TP, but had previously owned a PA-46-350. The flight instructor onboard reported that the pilot corrected to the right, which developed into a left-right oscillation during which the pilot was applying rudder input to each of the stops. Avionics data corroborated the flight instructor's account of the event. The available information suggests that the pilot over-controlled the airplane following the initial left veer.
The third event occurred a week after the first event when the pilot was receiving training in the airplane with a flight instructor. The airplane experienced a veer to the right during landing on runway 4 and the pilot reported that the right MLG departed the paved surface. The wind at the time of the incident was from 020º at 4 kts. The pilot recalled touching down with a left drift, so he applied increasing right rudder until the airplane responded and darted right. The instructor had his feet on the rudder pedals and reported that the pilot was adding right ridder before the NLG touched down and the airplane darted right once the NLG touched down. The instructor took the flight controls and regained control of the airplane. According to the instructor, the tire pressures were normal before the flight. Avionics data corroborated the instructor's account of the incident, with an initial slight left acceleration followed by a hard veer to the right. The available information suggests that the pilot applied right rudder before NLG touchdown instead of centering the NLG wheel. The airplane's pilot operating handbook contains a caution that states, 'In crosswind conditions, the nosewheel may not be aligned with the runway as the wheel touches down because of opposite rudder input. To prevent swerving in the direction the nosewheel is offset, the rudder must be promptly centered just as the nosewheel touches down.â Straightening the nose wheel can be challenging, especially when landing in crosswind conditions, since any amount of rudder input will also rotate the NLG wheel. The manufacturer has maintained that NLG tire pressure is critical for NLG steering control on the airplane. As the pressure decreases in the NLG tire, the contact patch with the runway increases and therefore, the friction force generated at the tire runway interface increases. The manufacturer recommends checking the tire pressure before each flight and has modified the specified pressure through service letter (SL) 1285, 1285A, and 1285B.
The rake angle of the NLG was established with the first PA-46 airplane and has not changed as the airplane has changed. The NLG rake is essentially zero, with the NLG strut designed to be 90º from the airplane longitudinal axis with a very tight tolerance allowing 0.5º forward rake and zero aft rake. This zero rake angle is good for static stability and taxiing at slower speeds, but can be problematic for its dynamic stability at higher speeds. A zero or aft rake can tend to cause the NLG tire to turn sharper without any input by the pilot. Low tire pressure can exacerbate the problem. On NLG touchdown, the NLG strut will deflect aft due to spring-back, increasing the negative rake that could cause an instability.
Any amount of play in the NLG steering system can result in pilots tending to overcontrol the airplane and input more rudder pedal before there is a response. The manufacturer has redesigned portions of the NLG steering system to tighten the tolerances and developed a new steering horn that attempts to minimize the play in the system by controlling the critical dimensions more closely. The new steering horn is being installed on all new airplanes after SN 4698135.
For the incidents investigated, there was not one single factor that could be identified as causal, but rather a combination of factors, such as tire pressure, rake angle, tolerance stack up, pilot technique, and crosswinds that combined to result in a directional excursion.
Probable Cause: The pilot's loss of directional control during landing in crosswind conditions. Contributing to the loss of control was the significantly underinflated nose landing gear tire.
Accident investigation:
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|
Sources:
NTSB ERA21LA065
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 02-May-2023 06:01 | ASN Update Bot | Added |
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