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Casualties unknown

Airplane Descends into Terrain During ILS Runway 31 Approach (N61568)

Ottumwa, IA, US

On August 6, 1991, a Cessna 172M (registration N61568) operated by Air Exec, Onc. was involved in an aviation accident near Ottumwa, IA. Investigators recorded the probable cause as: IMPROPER IFR PROCEDURE BY THE PILOT BY NOT MAINTAINING THE PROPER MINIMUM DESCENT ALTITUDE (MDA) UNTIL ESTABLISHED ON THE ILS LOCALIZER AND GLIDEPATH. 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 2026-07-04Data APIEditorial standards

During an ILS approach to runway 31, the airplane descended into trees and terrain 4.0 miles from the threshold and 0.19 mile left of centerline. No mechanical malfunction or significant weather was found.

Accident Details

The pilot was conducting an instrument landing system (ILS) approach to runway 31. During the approach, the airplane descended into trees and terrain, located inside the outer marker at a distance of 4.0 miles from the runway threshold and 0.19 mile to the left of the extended centerline. The initial impact occurred on a magnetic heading of 356 degrees at an elevation of 820 feet above mean sea level (MSL). The airport elevation is 845 feet MSL.

Approach Minimums

For the approach, the minimum descent altitude (MDA) before intercepting the ILS glide slope was 2,800 feet MSL. The MDA for a localizer-only approach was 1,200 feet MSL. The decision height (DH) for the ILS approach, if established on both the localizer and glidepath, was 1,041 feet MSL.

Investigation Findings

A subsequent investigation did not identify any mechanical malfunction of the aircraft or significant weather phenomena that would have resulted in the accident.

Controlled flight into terrain

Frequently asked questions

What happened in the 6 Aug 1991 Cessna 172M accident near Ottumwa, IA?

During an ILS approach to runway 31, the airplane descended into trees and terrain 4.0 miles from the threshold and 0.19 mile left of centerline. No mechanical malfunction or significant weather was found.

What aircraft was involved and where did it happen?

The accident on 6 Aug 1991 involved a Cessna 172M, registration N61568, operated by Air Exec, Onc., at Ottumwa, IA.

What was the probable cause of the accident?

IMPROPER IFR PROCEDURE BY THE PILOT BY NOT MAINTAINING THE PROPER MINIMUM DESCENT ALTITUDE (MDA) UNTIL ESTABLISHED ON THE ILS LOCALIZER AND GLIDEPATH.

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001212X17801. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.