Cessna 172L N9897G

Summary

On 10 October 2007 at about 17:14 local time, a Cessna 172L registered N9897G was involved in an accident near Prescott, Arizona, United States. One person was on board and one had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

10 October 2007 at 17:14

Classification

Accident

Location

Prescott, Arizona, United States

Coordinates

34.6544, -112.4194

Aircraft

Cessna 172L

Registration

N9897G

Category

Airplane

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Deer Valley → Prescott

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX08LA009

1 person had minor injuries.

The failure of maintenance personnel to detect fatigue cracks in the number 3 exhaust rocker arm, which lead to a partial loss of engine power.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

While in cruise flight, the engine had a sudden partial loss of power and made "clanging" noises. Although the engine continued to operate at a maximum of 900-1,100 revolutions per minute (rpm), insufficient power was available to maintain altitude. The pilot contacted the tower of a nearby airport, but determined that he would not be able to reach the runway. Due to power lines and a blind curve on a paved road, the pilot opted to land adjacent to the road. The airplane impacted a ditch and came to rest inverted. The engine had been overhauled 2.0 flight hours before the accident. A field overhaul had been performed on the engine due to a bent pushrod, stuck valve, and broken lifter for the number 3 cylinder. During the field overhaul, all four of the rocker arms had been magnetic particle inspected. Examination of the engine revealed that the number 3 cylinder exhaust rocker arm had separated into two pieces. A metallurgical examination was performed on the rocker arms by a Safety Board metallurgist. The number 3 exhaust rocker arm had fractured around the central pivot hole due to fatigue. The fatigue originated at the outer surface of the oil hole. The corners of the hole were sharp and had not been deburred, which increases the likelihood of fatigue cracking. The outer surface of the fatigued area was 0.31 inches long on the left side of the oil hole, and 0.21 inches long on the right side. The fractured exhaust rocker arm had been magnetic particle inspected for cracks during the field overhaul. The Safety Board metallurgist also noted staining on the cracks from the solution used during the magnetic particle inspection. Based on the staining, the cracks would have been detectable in size (about 0.2 inches) at the time of the inspection.

Quoted verbatim from the NTSB record.