Cessna 501 N804ST

Summary

On 24 May 2016 at about 02:56 local time, a Cessna 501 registered N804ST, operated by Eagle II Aero LLC, was involved in an accident near Texarkana, Arkansas, United States. 4 people were on board and 3 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

24 May 2016 at 02:56

Classification

Accident

Location

Texarkana, Arkansas, United States

Coordinates

33.4417, -94.0378

Aircraft

Cessna 501

Registration

N804ST

Category

Airplane

Year built

1980

Engines

2

Operator

Eagle II Aero LLC

Operating rule

Part 91: General Aviation

Purpose of flight

Executive/Corporate

Phase of flight

Not recorded

Route

Perryville → San Antonio

Aircraft damage

Substantial

Weather

VMC

Light

Night/Dark

NTSB number

CEN16LA197

3 people had minor injuries.

The pilot's failure to use supplemental oxygen as required during high-altitude flight, which resulted in his loss of consciousness following a loss of cabin pressurization. Contributing to the accident was the separation of the air conditioning system's primary pressurization duct and the subsequent failure of the aft pressure bulkhead check valve flapper due to progressive weakening from age.

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

Read the full NTSB narrative

The small jet airplane, which was being operated by a single pilot, experienced a loss of cabin pressurization during cruise flight about 43,000 ft. The pilot and passengers lost consciousness and the airplane entered an uncontrolled descent. The pilot regained consciousness and control of the airplane at 7,000 ft and landed the airplane at an alternate destination without further incident. The airplane sustained substantial damage to both wings due to the excessive aerodynamic loads incurred during the descent/recovery. Given the airplane's cruise altitude, the pilot was required by Federal Aviation Regulations to wear a supplemental oxygen mask; however, he was not doing so at the time of the loss of pressurization. Postaccident examination of the airplane revealed that the aft pressure bulkhead check valve flapper was fractured. Additionally, the air conditioning system's primary pressurization duct leading to the cabin was separated from its connection with the water separator due to a loose retaining clamp on the duct's metal worm-gear. Material analysis of the fractured flapper valve indicated the presence of progressive cracking and a loss of mechanical properties due to physical aging; exposure to atmospheric pollutants and oxygen can degrade the flapper material. The airplane lost pressurization when the air conditioning system's primary pressurization duct separated and the pressurized air was discharged into the unpressurized section of the airplane. The subsequent failure of the flapper valve then allowed the pressurized air to escape the cabin.  

Quoted verbatim from the NTSB record.