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Spoiled by the spoiler.

An F-14B Tomcat was on approach to an airfield for a full stop landing. The checklist was completed and all was normal until the aircraft passed the 45-degree position during the approach turn. The pilot felt and observed an uncommanded left roll and yaw. He countered this with opposite (right) stick and rudder. The radar intercept officer (RIO) in the rear seat saw that the port number four spoiler was fully deployed. The pilot initiated a waveoff, selecting military power with slightly less than a 10-degree pitch attitude while trimming nose down.

As the aircraft accelerated and angle of attack (AOA) was reduced, the aircraft became progressively harder to control and needed increasing right stick and rudder to maintain near-wings-level flight. The uncommanded left turn continued with increasing left angle of bank despite the pilot's applying full counter-control inputs.

At 240 knots, as the aircraft reached the 135-degree point during the downwind turn, the Tomcat continued to roll left through 100-degree angle of bank. The pilot then initiated ejection. The aircraft crashed and was destroyed but the pilot and RIO were not injured.

Grampaw Pettibone says:

Close call. It's as scary as it gets when you're down low and the bird wants to tip over despite maximum effort to keep it upright.

In this accident, investigators learned the spoiler actuator was corroded, resulting in the inadvertent and unexpected extension of the spoiler. Apart from exceeding the 225-knot airspeed limitation while in the landing configuration, the crew did well. The Tomcat might have handled a little better if they'd slowed down from 240 knots.

The investigators acquired new knowledge about the Tomcat from this accident. For example, wind tunnel testing after the mishap revealed a previously unidentified aerodynamic force: in one-G flight with flaps down configuration, the true AOA is negative when above 180 knots. In the negative AOA region, dihedral effect (roll due to sideslip) reverses. Right rudder inputs which normally result in right roll produce anywhere from no-roll moment to left-roll moment, depending on the AOA.

Anyway, regardless of the technicalities of 21st century aviation, the time-tested axiom--expect the unexpected--still applies. It's tough to honor this principle every minute of a sortie, but it's helpful to remember it when launching and recovering from shore or sea.

Gramps from Yesteryear

Illustrations by Ted Wilbur
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Title Annotation:Grampaw Pettibone
Author:Wilbur, Ted
Publication:Naval Aviation News
Geographic Code:1USA
Date:May 1, 2004
Previous Article:ANA photo contest.
Next Article:Fly by wire.

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