Helicopter accident Norway - the Foreigner

EASA orders Super Puma inspections

TEXT: Michael Sandelson – The Foreigner ©2016

http://theforeigner.no/pages/news/easa-orders-super-puma-inspections/

The European Air Safety Agency’s Emergency Airworthiness Directive covers mandatory inspection of key EC 225 helicopter parts. Airbus Helicopters also tells aircraft owners to take action.

In their document, officials say that their move is a precautionary measure following the 29th April accident in Norway, which claimed 13 lives.

Norway’s Accident Investigation Board (NAIB) has stated that the crash was due to technical failure rather than human error.

NAIB officials are upholding their own temporary ban on Airbus EC225 LP flights. The UK and Norwegian CAAs have issued No Fly orders.

Airbus Helicopters has concurred with the decision to ground all commercial flights using this type of aircraft.

“The partial information available so far indicates in-flight separation of the main rotor hub from the main gearbox,” the European Air Safety Agency’s Airworthiness Directive reads.

Technical failure investigation

The root cause of the accident in Norway is still under investigation. EASA states that it may require further mandatory action.

In a statement, Airbus Helicopters says that “the investigation will now solely be focused on potential root causes of a technical failure, such as design, production, and/or maintenance.”

Current main rotor drive inspections EASA has imposed on all owners of this aircraft type must be carried out before the helicopters’ next flights, they say.

These relate to:        

·         Checking that all the main gearbox’s (MGB) suspension bars – Front and Right Hand and Left Hand – are installed correctly (these are the MGB’s mounting supports). This is in accordance with Airbus Helicopter’s (AH) instructions in their EC225 Alert Service Bulletin 53A058

·         Checking that there are no metal particles in the MGB’s chip detectors – in accordance with the instructions of Work Card 60.00.00.212 of AH EC225 Maintenance Manual (MMA)

·         Checking that there are no metal particles in the MGB’s oil filter. This is in accordance with the instructions of Work Card 63.24.01.061 of AH EC 225 MMA

·         Checking that no limits have been exceeded on helicopters that are fitted with an M’ARMS Vibration Health Monitoring System. The data is to be accessible should future analysis be needed.

Critical part        

Commenting on EASA’s Emergency Airworthiness Directive, Per Gram, a former helicopter pilot with over 20,000 hours flying time tells The Foreigner that “the entire helicopter hangs underneath these MGB suspension bars.”

“The three suspension bars run from the fuselage up to the main gearbox and connect everything together. The main rotor loosens if the Front Suspension Bar either fails or comes off. It’s quite obvious why investigators are focusing on this issue now,” he adds.

EASA’s Directive refers to a previous “Service Bulletin” that was issued with regards to the MGB’s mounting supports.

These are issued by aircraft manufacturers every so often and usually require all operators to check for specific damage or wrongly fitted components after something minor has been found during routine maintenance on a particular aircraft.

Airbus Helicopters has also sent out an Emergency Air Service Bulletin (Airbus Safety Alert 3035-S-00, dated 3rd May 2016) to all EC 225 (now H225) owners.

“Following the accident involving an EC225LP dated April 29th, and considering the observations gathered by the investigation team since this date, this Alert Service Bulletin requests, as a precautionary measure, the verification of the correct installation of all MGB suspension bar attachments,” they write.

“This Alert Service Bulletin consists in a one-off check of the MGB suspension bar attachments for their torque tightening value and the condition of the pins and sending the results of this check to Airbus Helicopters. Compliance with this Alert Service Bulletin is mandatory.”

Close examination

Chip detectors are magnetic switches that protrude into the flow of oil in engines and gearboxes, usually situated near the oil filter. 

The oil should not usually contain any metal particles during normal operation, but small particles of metal will break off and get into the oil if a component is beginning to wear badly or break up.

These then stick to the magnet of the chip detector as they flow past it and will short out the two contacts, thereby setting off an alarm to the pilot that something is wrong.

The two Maintenance Manual references will refer to the manufacturer’s instructions describing the correct procedure to the engineers for removing and inspecting these components.

 

Oil filter checks are routinely made every time an oil change is done on an aircraft, but can also be called for in a case where an investigation is being made into a potential failure situation. 

The oil filter is removed and replaced and the old filter is then sent off to a specialist company to be analysed. 

They cut the filter open and make a spectroscopic analysis of any particles that are found in the filter paper to accurately determine the chemical composition of the particles. 

Experts may also make a similar analysis on a sample of the oil – often referred to as a Spectrometic Oil Analysis Program (SOAP) sample. 

In-flight alarms

If any particles are found in the oil, this test will reveal exactly what metal or alloy they are made of, and this data can be used by the aircraft manufacturer to determine exactly which component in an engine or gearbox they are likely to have come from. 

These tests are routinely made every time the oil is changed in aircraft engines and gearboxes, and usually allow component failures to be detected long before they become serious.

M’ARMS Vibration Health Monitoring System stands for “Aircraft Recording and Monitoring System”. It is an electronic vibration detector fitted to some aircraft engines and gearboxes in order to alert the crew to abnormal vibration in the engine or gearbox.

The system, which is not fitted to all aircraft, will give the crew additional information about the seriousness of any engine or gearbox-related problem should another indication alarm (such as a chip detector) go off during flight. 

Data from this will most likely be recorded on the aircraft’s flight data recorder as well. 

The M’ARMS system is also useful because it records vibration and engine exceedance data (i.e. if the engine has been mistreated by over-speeding, or over-torqueing, etc.) on previous flights.

Airbus Helicopters says that it “welcomes the announcement made by the Accident Investigation Board Norway (AIBN) and “continues to provide its full support to the AIBN investigation.”