CHIEF WARRANT OFFICER 2 ASHTON COOPRIDER
10th Combat Aviation Brigade
Fort Drum, New York

Author’s note: I was a troop pilot with about 400 hours, flying with a squadron instructor pilot (IP) with more than 1,000 hours. Our AH-64D Apache Longbow was equipped with full fuel tanks (including the integrated auxiliary fuel system), one Hellfire missile launcher, one rocket pod and a fire control radar. The IP was flying into the last-third of his duty day, while I was well into the second-third of mine. While conducting pilot in command (PC) preparation training, we encountered loss of tail rotor effectiveness (LTE) while attempting to land during terrain flight at night utilizing the Apache’s night vision systems. The event occurred during the second half of a four-hour flight about 2300 local time within our local training range in the vicinity of a medium-sized remote training area. Winds were from the south at approximately 10-20 knots.

The mission began with a midday show for a day-out, night-return flight. The IP had conducted squadron-level administrative duties before arriving for flight duty. As such, we briefed the Risk Common Operating Picture for flight into the last-third of our duty days. As the co-pilot and PC candidate, I showed up for preflight administrative duties about four hours prior to takeoff. The primary factor dictating our mission plan was forecasted high winds; however, the weather was otherwise favorable, so we decided to go. We would begin our flight at higher altitudes and continue to descend once comfortable.

After conducting daylight terrain flight maneuvers and returning to the airfield to refuel, we departed for the night portion of the mission. Just after departure, we proceeded to a well-known terrain flight training area and began to shoot approaches. Winds during the daytime portion were assessed and confirmed to be consistently high and from the south. I took this into consideration as we descended toward the terrain and maintained a greater airspeed to mitigate the effects of the wind.

As the midpoint of the second period neared, while attempting to fly a terrain flight approach in a low-airspeed, high-weight, high-power setting profile, I initiated a right base turn away from a quartering left to direct tailwind. As the wind came off the tail and began to drag the nose to the right while pulling the tail left (weathervane effect), I instinctually moved to catch the right yaw with left pedal and noticed the aircraft torque setting was rapidly approaching 100 percent. I attempted to lower the nose and gain airspeed to fly out of the condition and gain a greater power margin, but I was hesitant to enter a time-limited torque range, which caused me to incur an appreciable rate of descent.

The nose continued to weathervane to the right in search of the wind, and the aircraft began a turning descent toward the treetops. My ability to interpret symbology then began to deteriorate as I focused intently on not overtorquing the aircraft. This resulted in a slowing of the aircraft such that we began to trend toward an out-of-ground-effect hover with limited remaining power to arrest our descent.

As the aircraft’s nose passed through 180 degrees of yaw, I queried the IP to assess the situation and we began increasing power while further lowering the nose and pulling through the turn to gain airspeed and eventually establish a climb. Once this was accomplished and the nose passed through about 270 degrees, the aircraft was oriented into the wind and able to level off. A few moments later, we were able to decrease the power setting and initiate a climb to terminate terrain flight operations. We decided to re-cage and assessed the situation.

At this point, I made the decision to discontinue training for the night and advised that we return to base. We both concurred during the mission debrief that a prime contributing factor to the manifestation of this condition was our combined fatigue level. While it’s important to widen your personal limitations in training, consider doing so while mentally fresh. It is also important to continually consider your absolute maximum power available on the day and to realize that its use may be required in an emergency. Regarding LTE, it is important to place emphasis on avoidance, perhaps even more so than on recovery.

Lessons learned

Once we arrived safely at home base, we had a thorough discussion concerning what happened during the flight and what we should consider more thoroughly moving forward. The following are a few tactics, techniques and procedures that may help to mitigate the inherent risks of operating our aircraft during high-wind conditions and under higher levels of fatigue as required by the mission.

1. Review and brief directional control margin (AH-64D/E) considerations during your crew brief prior to operations in high wind. Take care to chair fly an LTE recovery during the discussion. Discuss how maximum continuous power available and time-limited power available relate to one another. If available, emphasize the availability of greater power under certain circumstances!
2. Brief wind direction and magnitude during final approach to land and consider the effect of wind on directional authority during each phase of flight. If necessary, initiate go-arounds early.
3. When able, consider making turns to the left when operating in conditions conducive to LTE (for counterclockwise-rotating helicopters). Avoid turning away from high winds when operating in low-altitude, high-power settings and low-airspeed flight profiles.
4. Consider the benefits of operating the stabilator manually to reduce the likelihood of it becoming caught in the wind.

 

FYI

Since the beginning of FY23, there have been seven aviation mishaps associated with loss of tail rotor effectiveness (LTE). If your aircrew experiences LTE and recovers from it, the U.S. Army Combat Readiness Center needs you to report it as a near miss. We must capture all data possible so we can learn from and stop this trend.

 

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• 4 August 2024
• [EasyDNNnewsLocalizedText:Author]: USACRC Editor
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