75 knots seems way to fast to contact the ground on a non prepared surface. It almost makes you wonder if the pilots were trying to wave off their approach and contacted the ground in the process.
Exactly.
Concur, carrying 75 kts into most LZ’s is not going to generally turn out well. One would do that on prepared hard surfaces. In CH-46’s we called this “powered descending flight” this was where the weight of the aircraft exceeded the lift being produced, usually as a result of a engine failure. It sounds from the limited details that they were attempting a downwind landing, this did not help their cause any. They may have thought that they could get some help with ground effect but with a high sink rate that would not have been an option. With rotor speed decaying, they could have transitioned back to fixed wing mode, this might not have been an option for them. I recall reading a while back that there were engine issues in Iraq and Afghanistan.
75 knots seems way to fast to contact the ground on a non prepared surface. It almost makes you wonder if the pilots were trying to wave off their approach and contacted the ground in the process.
After reading the entire AIB report, I found the following:
I considered engine percent performance, which was last measured on 6 April 2010 (99.5% for the left engine and 95.3% for the right engine). The MA performed four austere landings, including one with a left engine air particle separator failure, after that 6 April 2010 measurement. (Tab D-4, Tab U-5 thru U-6, Tab V-59.3, Tab BB-64, Tab II-3, II-52) Degraded engines could have led to engine failure, surge/stall or insufficient power when a high power demand was required. I determined, by the greater weight of credible evidence, that one or both of the MA’s engines was degraded below acceptable standards.
And:
There was a new software update to the CV-22 systems just prior to active use on this deployment. (Tab V-2.8) One of the new features of this software was an increase in cruising speed while in airplane mode. A familiar TCL setting for a specific airspeed would now result in a higher air speed. (Tab V-2.8, Tab II-6, Tab JJ-51 thru JJ-52) The MA was at an excessive speed in the final phases of flight. (Tab L-4, Tab J-21 to J-22, Tab Z-27) There is no direct evidence, but it is possible that the MP reverted to learned behavior from numerous missions in the CV-22 prior to the software update, resulting in a higher speed during the approach to the LZ.
But what really caught my eye early in the report, and was never fully explained was this:
From 2008:58Z to 2009:08Z, the MA’s total fuel value decreased by 74 pounds, which equates to a rate of 26,640 pounds per hour. (Tab JJ-41 thru JJ-49) The engines are capable of commanding a maximum burn rate of 6,000 pounds per hour. (Tab JJ-49) The A-10 video of the last 20 seconds of the mishap flight showed a substance trailing the MA starting at approximately 2008:57Z. (Tab Z-27, Tab HH-25 thru HH-31) Two separate trails remained behind the MA for several seconds. This occurred several times up until approximately 2009:12Z, which was three seconds before ground impact. A very excited discussion occurred in the cockpit seconds prior to impact. (Tab V-60.28 thru V-60.29, V-60.36, V-72.1) A member of the MCR counted down “10, 9, 8, 7” rapidly and at “7” the aircraft impacted the ground. (Tab V-20.4) MTS heard several aircraft generated voice warnings upon impact. (Tab V-60.22)
What accounted for the fuel use rate 4 1/2 times higher than the maximum engine fuel burn rate? Could a fuel leak have caused reduced engine performance? Not a thing about this fuel rate issue appeared in the conclusions.