Evidence of volcanic ash and water contamination : Air Nippon flight EH2142

Air Nippon flight EH2142 : on July 5 (Wednesday), 2006 at 07:24 JST, a Boeing 737-500 airplane, JA8419, operated by Air Nippon Co., Ltd. took off Fukuoka Airport as All Nippon Airways scheduled flight 2142.

At about 08:10, while flying at approximately 37,000 ft approximately 60 nm southeast of Kushimoto VORTAC, a cabin depressurization warning was displayed and the oxygen masks in the cabin were automatically deployed.

The aircraft made an emergency descent and, at 09:09, landed on Chubu International Airport. Of the 46 persons on board the aircraft, including the Pilot in Command, 4 other crewmembers and 41 passengers, no one was injured.

while Air Nippon flight EH2142 was cruising at FL370, the master caution light and the system annunciator’s “AIR COND” light illuminated in the cockpit.

It is estimated that this serious incident would have occurred through the following process: the aircraft encountered turbulence when flying at FL370, quickly reduced the engine power in order to avoid excessive airspeed, and this in turn caused a change of the source of bleed air, which resulted in bleed air with higher temperature flowing into the pre-coolers, but the bleed air was not cooled sufficiently, and the overheat switches activated, closing the bleed valves for both systems and thus preventing the air supply necessary for pressurization of aircraft, ultimately resulting in an abnormal cabin depressurization.

It is estimated that the overheat switches activated because the operation of the control valves (PCVs) was sluggish due to contamination.

It is estimated that contamination deposits on the bleed related valves and other components resulted from incomplete draining of water and detergent which entered these components in large quantities during water washing conducted for engine gas path cleaning.