In-Flight Propeller Blade Separation Leads to Gear-Up Landing (N66LA)

Q: What aircraft was involved and where did it happen?

The accident on 1992-08-18 involved a Mitsubishi MU-2-60, registration N66LA, operated by Epps Air Service, at Philadelphia, PA.

On August 18, 1992, a Mitsubishi MU-2-60 (registration N66LA) operated by Epps Air Service was involved in an aviation accident near Philadelphia, PA. Investigators recorded the probable cause as: Fatigue cracking initiated from multiple sites at corrosion pits in the balancing hole of the propeller blade; the corrosion pitting was not detected during the last overhaul, and procedures to shot peen and paint the balancing hole were not performed. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 1781061362Data API Editorial standards

A propeller blade separated from the left propeller assembly during cruise at 6,000 ft MSL, penetrating the fuselage and causing electrical loss. The pilot flew for 40 minutes in IMC without electrical power before performing a gear-up landing.

Incident Overview

While in cruise flight at 6,000 feet MSL, a propeller blade from the left propeller assembly separated in-flight. The separated blade penetrated the fuselage, breaking electrical lines and causing a loss of electrical power. At the time, the airplane was operating in instrument meteorological conditions (IMC).

Pilot Actions

Following the loss of electrical power, the pilot elected to execute a 180-degree turn in an attempt to fly to an area of better weather. The pilot flew without electrical power and without most of the instruments for approximately 40 minutes until reaching an area of clear weather. Once the pilot was able to identify his location, he elected to perform a gear-up landing at the nearest airport.

Metallurgical Examination

Metallurgical examination of the separated blade revealed that the separation was the result of fatigue cracking. The fatigue cracking initiated from multiple sites located at corrosion pits in the balancing hole. It was determined that the corrosion pitting had not been detected during the last overhaul, and procedures to shot peen and paint the balancing hole were not performed.

Probable cause

Fatigue cracking initiated from multiple sites at corrosion pits in the balancing hole of the propeller blade; the corrosion pitting was not detected during the last overhaul, and procedures to shot peen and paint the balancing hole were not performed.

Structural failure

1992-08-18: Mitsubishi MU-2-60 (N66LA) — Epps Air Service — Philadelphia, PA