2002 Ad

Flying Safety, Jan-Feb, 2003 by Greg Small

In FY02, the Air Force experienced nine Class A UAV Flight Mishaps. Five of these were Predators, two were Global Hawks and two were QF-4E Drones. UAV mishaps have not been addressed in previous annual mishap review editions of this publication, as they do not impact the overall USAF flight mishap rate. That may change in the near future, so it is our intent with this article to introduce the readers to some of the more significant mishaps.

Global Hawk

One of the Global Hawks was returning from a truncated operational mission in support of Operation ENDURING FREEDOM when it departed controlled flight, entering an unrecoverable right spin. It impacted the ground in an uninhabited area approximately 80 miles south of the classified Forward Operating Location landing site. The damage to the Mishap Aircraft (MA), including the sensor package, was estimated at $40.6 million.

During the return flight, the right outboard ruddervator actuator control rod failed, allowing the ruddervator to travel unrestrained beyond its normal range. The control rod failure was caused by metal fatigue induced by a bend in the rod that occurred when it contacted an improperly installed actuator nut plate bolt. While the MA was descending through approximately 54,000 feet MSL during the second of three 90-degree planned left turns, the lift spoilers fully deployed to assist the descent. Twenty-nine seconds later, the MA departed controlled flight, entering a right spin.

Once the four lift spoilers were raised to their maximum 45-degree deflection at this altitude, the ensuing turbulent air induced violent flutter on the unconstrained right outboard ruddervator. The energy of the resultant flutter was absorbed by the right V-tail main spar, and quickly resulted in delamination of the spar caps and center webbing from the root to over one-third the length of the spar. The flexing of the spar and continuing flutter eventually caused failure of the double torsion box construction of the right V-tail, further subjecting the V-tail to increasing torsional loading. The overall result was the structural failure of the right V-tail inducing the right spin.

Predator

A mishap occurred in Operation ENDURING FREEDOM during a planned handoff of control between two ground control stations using a lost link recovery orbit point. When accomplishing this lost link handover, the mishap crew failed to accomplish checklist steps in the proper order, resulting in the MA's Stability Augmentation System (SAS) and engine ignition being turned off immediately after enabling the satellite command link. When the MA received the commands to turn the SAS and the engine off, it entered an uncommanded dive. The MA impacted the ground nine miles off the end of the runway of the classified Forward Operating Location and was destroyed. The loss was estimated at $3,251,400.

In a second OEF Predator mishap, the MA crashed while landing at a classified Forward Operating Location. The mishap pilot's (MP) first attempted landing resulted in a go-around due to the effects of gusty winds. During the second approach under similar wind conditions, the MA's nose ballooned in the flare. The MP attempted to push the nose forward to correct this condition. Before he had the opportunity to initiate go-around procedures again, the MA's nose pitched forward beyond his control. The nose gear struck the runway with excessive force, breaking the nose landing gear strut. As an additional result of the excessively hard landing, the MA's right tailplane separated from the fuselage. The resulting asymmetrical pitch and yaw caused the MA to bank sharply to the right. It impacted the ground approximately 100 yards east of the runway and was destroyed. The primary cause of the mishap was the MP's inability to maintain positive control of the aircraft due to the adverse effects of strong wind gusts. The resulting structural damage from a nose gear-first landing further inhibited control of the aircraft, which then impacted the ground. Gust wind speeds reported just prior to the mishap were at the maximum limit for Predator landings. Gusts five minutes after the mishap were out of limits.

We lost another Predator when it experienced a catastrophic engine failure while conducting a mission in support of Operation SOUTHERN WATCH. The Mishap Crew recognized an engine malfunction approximately two hours after takeoff and immediately initiated an RTB. As the MA approached the airfield, the engine malfunction became catastrophic, causing an engine failure and seizure that negated all possibility of a safe landing. The crew diverted the MA to an unprepared landing surface. The MA suffered extreme damage upon impact, primarily to the landing gear and payload. The loss is valued at almost $1.5 million.

Drones

The first of two QF-4E Class A flight mishaps occurred during a planned automatic takeoff (ATO) using the automatic flight control system (AFCS). During takeoff roll the MA began to experience slight but increasing negative and positive pitch oscillations. These continued as the MA commenced rotation, pitching up initially to 14.5 degrees nose-high and then pitching down to -20.3 degrees nose-low, ultimately causing the MA to impact the runway. The MA was destroyed upon impact and the resulting post-crash fire. The tri-axis rate gyro, which provides pitch, roll and yaw rate information to the AFCS executing the ATO, was incorrectly installed.