An air accident occurred at 16:30 on Friday 29 September 2007 at Sipoonlahti, west of the city of Porvoo. A Cessna 172N, registration OH-CAU, owned by the Malmi Aviation Club made an emergency landing on Porvoo motorway, close to the Sipoonlahti exit. In addition to the pilot there were two passengers onboard. No-one was injured; however, the aircraft sustained major damage. The incident caused no harm to road traffic. The aircraft was fitted with a TAE 125-01 diesel engine and the aircraft used JET A1 jet engine fuel.

Accident Investigation Board Finland (AIB) appointed investigation commission C7/2007L for this accident. Investigator Jouko Koskimies was named investigator-in-charge, accompanied by the former Chief Accident Investigator Esko Lähteenmäki and Air Accident Investigator Tii-Maria Siitonen as members of the commission.

OH-CAU departed Helsinki-Malmi aerodrome at 16:16 for a local flight over Sipoonlahti bay. Meteorological conditions were good. The flight headed towards the edge of the Porvoo oil refinery protection zone via reporting point “Deger”. Altitude was 900 FT and airspeed was 100 KT at 75 % cruising power. Engine power suddenly decreased to 25−30 % east of Sipoonlahti bay. The pilot immediately turned left towards the village of Box and at 16:27 he reported the loss of engine power to Malmi air traffic control. Malmi ATC cleared OH-CAU for the Control Zone with a heading directly towards the aerodrome and launched the appropriate emergency procedures.

At 16:28 the pilot informed the ATC that engine power was now at only 31 %. A moment later he realized that they would not make it to Malmi and decided to make an emergency landing on the motorway instead. Dense road traffic prevented a landing before the Hangelby Bridge. Therefore, the pilot landed on the right hand lane of the motorway leading to the Sipoonlahti exit.

Touchdown occurred approximately 250 m past Hangelby Bridge. The pilot was unable to stop the aircraft before the exit ramp. The right wing collided with a light pole on the right side of the road, followed by the left wing hitting a traffic sign at the onset of the ramp. The left main undercarriage straddled the crash barrier, the nose gear broke off, the nose of the aircraft fell and the propeller blades broke as they hit the crash barrier.

At 16:28 the air traffic controller declared an aviation emergency to the Emergency Response Centre and the aerodrome fire department. Rescue units were alerted between 16:33−16:36 and the first units arrived at the accident site at 16:42. The police performed a breathalyzer test on the pilot at 17:10. The result indicated zero blood alcohol.

When the engine was later inspected metal shavings were detected in the fuel system. The damaged high-pressure (HP) fuel pump was found to be the source of the shavings. The fuel system parts were sent to the engine manufacturer in Germany. The fuel was analysed in Finland and in Germany and it was found to meet the requirements set for JET A1.

JET A1 is refined to be a jet engine fuel. Its lubricity is significantly inferior to that of diesel fuel. The lubricity of JET A1 is measured with the Ball-On Cylinder Lubricity Evaluator (BOCLE) test method. The highest permissible BOCLE value is set at 0.850 mm.

The High Frequency Reciprocating Rig (HFRR) test method evaluates the lubricity of diesel fuel. The highest permissible value is set at 0.460 mm. JET A1 is not tested with the HFRR method; nor are there any internationally accepted HFRR value requirements for this fuel. The values derived from BOCLE and HFRR testing are mutually incompatible.

The values denote the size of the wear scar generated on the tested surface. Low values indicate high lubricity.

The HFRR value of the fuel used was measured at 0.835 mm. The European Aviation Safety Agency (EASA) informed the commission that the HFRR value of the fuel used in this type of HP pump’s certification testing is 0.780 mm.

The accident was caused by a chain of events. The damage to the HP fuel pump caused the common rail pressure control valve to jam almost fully open. This caused the power loss because the remaining fuel pressure in the common rail could only sustain idle power. A metal shaving from the damaged HP fuel pump eccentric cam bearing surface probably caused the pressure-control valve ball to remain open. The damage on the eccentric cam bearing surface has initiated several flight hours earlier. The damage has caused by water in the fuel. The water has probably come via the loose fuel filler cap. There was no water in the fuel samples taken prior and after to the accident flight.

The investigation commission recommended that EASA take action to establish whether JET A1 can safely be used as aircraft diesel engine fuel, and if it can, the required measures. In addition, the investigation commission recommended that EASA consider whether a new type certificate test be required for TAE engine high-pressure fuel pumps, using such JET A1 fuel which meets the lowest permissible lubricity value set for jet engine fuel. Further the investigation commission recommended that EASA take action to ensure that required maintenance instructions will be published concerning the fuel tank filler caps adjustment on the aircraft equipped with TAE-engines.

Download here the investigation report, pdf-file, 344 kB