For this accident, VRS is not a likely factor, however, taking eyewitness accounts to narrow the scope of the investigation is not a great plan. The clutch and the VRS-related power fluctuations do have potential to be related. The envelope for VRS is well established, and should not 20 years later be a factor, but it was raised in the posts.
Do you suggest that a Prop-Rotor departed in flight? What is the source of that information? The Japanese PM noted that the left engine was apparently "on fire" and a later report indicated that the aircraft rolled over "180" degrees" to being upside down. Those are consistent with a failure of drive, and that comes back to anything that relatest to torque transfer to the prop rotor, which includes the clutch system. There have been enough hard engagements to be of concern, and the consequences of a hard engagement can include a loss of drive to the rotor, which has a fair chance of spoiling everyone's day.
Autorotation is not covered in the MV22 NATOPS or PCL, Perhaps the dash-1 covers something in that area. The suggested power-off sink rate of 18 m/sec is fairly impressive. The 609 and XV-3 were autorotated, the XV-15 had the blade tested in the wind tunnel at NASA Ames, and was estimated to have a sink of 2400 fpm... At 60-80 kias, 18 m/sec is a mighty steep descent. Auto is moot if they are upside down, which suggests a transmission failure assuming that in straight and level cruise it is pretty hard to get into VRS. A drive failure spoils their day and is consistent with reported events.
I think that the V-22 is a neat aircraft, but it has issues, the transmission/clutch is one matter, and the remote possibility of autorotation doesn't make for comfort in a combat aircraft. The IFR handling is tolerable and while it may occasionally be marginal according to the flight test reports early on in some phases, it is within acceptable standards.
[1] Maisel, M. D., Giulianetti, D. J., & Dugan, D. C. (2000). The History of the XV-15 Tilt Rotor Research Aircraft: From Concept to Flight.
[2] REPORT 301-099-005 NASA CONTRACT NAS2-8580. (1976). WIND TUNNEL TEST RESULTS OF 25-FOOT TILT ROTOR DURING AUTOROTATION.
[3] A1-V22AB-NFM-000 NATOPS FLIGHT MANUAL NAVY MODEL MV-22B TILTROTOR
[4] A1-V22AB-NFM-500 NATOPS PILOT’S/ AIRCREW POCKET CHECKLIST MV-22B TILTROTOR
[5] Trail, S. B. (2006). Evaluation of V-22 Tiltrotor Handling Qualities in the Instrument Evaluation of V-22 Tiltrotor Handling Qualities in the Instrument Meteorological Environment Meteorological Environment.
[5] 1-V22AB-NFM-500A1-V22AB-NFM-500
Last edited by fdr; 24th Dec 2023 at 07:51.