By Carl Ziegler, A&P/IA

I’ve put my inspector hat on today. In this article, we’re going to look at several defining accidents that occurred during the first half of the year.

Accident #1

This first narrative pertains to an accident that happened in February of this year. It was fatal for one person and injured four others. This accident involved a Learjet 35 that was landing in Scottsdale, Arizona. News and witnesses reported the aircraft veered to the left off the runway after touchdown and struck another jet parked on the ramp. It didn’t take long for the NTSB to determine the sequence of events from video footage and the trail of parts and intact wreckage.

The net cause of this accident was the left landing gear be­coming detached from its fittings in the left wheel well. Sub­sequent investigation by the NTSB showed that the aft trun­nion pin had migrated out of the landing gear and allowed the gear to swing in the wind when the pilot selected gear down. The mechanic had failed to verify that the retaining bolt was stabbed thru the trunnion pin. The flight crew was totally unaware of the impending disaster about to unfold. This particular accident has been nagging me all year and formed the impetus for this article.

Here is a brief NTSB summary of the mechanics of this event.

Accident #1. These images were taken by a bystander, but are included in the NTSB report. They demonstrate that the landing gear the day of the accident did not deploy properly.

According to the NTSB report, the procedure to reinstall the gear must be followed explicitly. “If the [retaining] bolt is secured before engaging the pin in the trunnion casing, then the grease hole could be aft of the bushing, allowing grease to escape outside the pin, into the wing bay behind spar #7,” the NTSB said. “With the adjacent access panel removed, using a mirror, the pin can visibly be seen not making contact with the aft trunnion fitting when it is not fully pushed into the trunnion casing.”

Notably, the NTSB is aware of at least three other previous events where Learjet landing gear had disconnected from the airframe be­cause the retaining bolt was not en­gaged through the aft trunnion pin.

Accident #1. Let’s play stab the pin. It might be rocket science to verify you stabbed the trunnion bolt. This diagram shows the assembly and importance of the retaining bolt placed through the trunnion pin.
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Carl has close to 50 years of continuous experience working as an aircraft technician and 38 years as an IA. In addition to GA, he has acquired over 38 years of airline experience with Northwest and most recently with Delta, finishing his last 13 years of airline service as an aircraft inspector. He currently flies a 1976 Cessna 172N.