EASA & FAA HUMS / VHM Developments

EASA & FAA HUMS / VHM Developments

More information has emerged on European Aviation Safety Agency (EASA) and Federal Aviation Administration (FAA) Health and Usage Monitoring Systems (HUMS) / Vibration Health Monitoring (VHM) initiatives.

EASA HUMS / VHM Research

There was more detail on HUMS/VHM research that Aerossurance has previously reported on when Cranfield University’s Matt Greaves presented the results of research project EASA.2012.OP.13 VHM at EASA’s 8th Rotorcraft Symposium last month in Cologne.

The research included fault tree analysis (FTA) on 12 carefully selected accident case studies:

• SA330J 9M-SSC in 1980 (Main Gear Box [MGB] epicyclic failure)
• S-61N G-ASNL in 1983 (MGB failure)
• AS332L1 LN-OPG in 1997 (High Speed Shaft Failure)
• S-76A+ G-BJVX in 2001 (Main Rotor Blade [MRB] failure)
• S-61N G-BBHM in 2002 (Engine Oil Fire/Structural Failure)
• S-61N C-FHHD in 2002 (MGB failure after oil loss and fire)
• AS332L2 G-JSAR in 2003 (Accessory Gear Box [AGB] failure)
• AS332L G-PUMI in 2006 (Main Rotor Spindle crack)
• AS332L2 G-CHCF in 2007 (Freewheel Unit [FWU] failure)
• S-92A C-GZCH in 2009 (MGB failure after oil loss)
• AS332L2 G-REDL in 2009 (MGB epicyclic failure)
• EC225s G-REDW/G-CHCN in 2012 (MGB shaft failure)

The focus then turned to one of the most demanding locations to place a sensor, an MGB epicyclic module.

This drove the use of high frequency stress wave sensors, known by the slightly misleading title of ‘Acoustic Emission’ (AE) sensors.  These were coupled with wireless transmission of data from within the epicyclic casing and tested on a test rig at Cranfield and full scale on an ex-Royal Air Force SA330 Puma HC1 gearbox at an Airbus Helicopters’ test facility.

Greaves’ presentation is downloadable as part of a large zip file for the whole symposium or directly here 2.2._Greaves_Results from EASA project 2012.OP.13 – VHM.  An earlier paper presented to the International Society of Air Safety Investigators (ISASI) annual conference was discussed in detail by Aerossurance in October.  The full research report is due out early in 2015.

Late in 2014 EASA has also issued a call for tender for a follow on project EASA.2014.OP.15, Helicopter main gearbox health (MGH), discussed further by Aerossurance here.

EASA has already launched a programme of gearbox lubrication rule making, previously discussed by Aerossurance and influenced by the S-92A C-GZCH accident offshore Canada in 2009.

UPDATE 9 May 2017: The Cranfield University report on EASA research project EASA.2012.OP.13 VHM which followed G-REDL is now available at: EASA_REP_RESEA_2012_6 Vibration Health Monitoring or Alternative Techniques for Helicopters

EASA Certification Memo on the Prioritisation of Maintenance Alerts

Just before Christmas EASA issued a draft Certification Memo (Proposed CM-DASA-001 Issue 01) for consultation.  The document would provide non-binding guidance on the Prioritisation of Maintenance Alerts from HUMS / VHM systems and supplements EASA CS-29 requirement CS-29.1465.  Here an ‘Alert’ is a VHM indication that requires further investigation to determine if corrective maintenance action is necessary and an ‘Alarm’ is a alert that did indeed need corrective maintenance action.

CS-29.1465 is the certification requirement for the approval of HUMS / VHM systems either when requested by the applicant, meet an operational requirement or as a ‘compensating provision’ as a result of a 29.917(b)/29.547(b) design assessment.   It was developed by an EASA/FAA/Industry Rotorcraft VHM Working Group (RVHMWG), picking up work that had been started by the UK CAA’s Helicopter Health Monitoring Working Group (HHMAG).  Following the issue of NPA2010/12, this requirement was introduced into CS-29 at Amendment 3 in late 2012. It is unique to CS-29 and does not feature in the FAA’s FAR-29.

In the Proposed CM EASA state:

Service experience over recent years has shown that it is beneficial to have some form of prioritisation hierarchy of Alerts, in order to show which are the most significant and / or urgent.

EASA are proposing a convention of:

1. Red for ‘Level 1 Alerts’ that require action prior to the next flight.

2. Yellow or Amber for ‘Level 2 Alerts’ that require maintenance personnel awareness, but do not preclude continued operation.

3. A third, distinct colour of the applicant’s choice, for ‘Advisory’ conditions that ‘may influence future maintenance’.

The Proposed CM is open for public consultation in open until 28 January 2015.

UPDATE 2 July 2015: The Certification Memo has been issued at Issue 1 Rev 00 after comments contained in the Comment Review Document were analysed.

FAA HUMS / VHM Research and Review of MG15

The FAA’s Andy Shaw also presented at EASA’s 8th Rotorcraft Symposium last month.  His presentation covered three topics: HUMS, ADS-B and use of the Non-Required Safety Enhancing Equipment (NORSEE) approval route.

In just three slides on HUMS, Shaw briefly discussed a long term programme of FAA HUMS research.  This work included the verification and validation of flight Regime Recognition Algorithms (RRA) and HUMS for usage credit.  This used RRA and with crack growth modelling to calculate a Remaining Useful Life (RUL).  It is noteworthy that the research focus is more on ‘usage’ than ‘health’ applications.  It was revealed that the FAA is assessing two ‘HUMS for credit’ proposals from rotorcraft OEMs.

In the UK, Aerossurance has been working on a 2 year HUMS Maintenance Credit Project for the UK Military Aviation Authority (MAA) since September 2014.

Shaw also reported that this year the FAA will evaluate lessons from this research reports for applicability to AC 29-2 MG-15. Miscellaneous Guidance 15 was introduced to AC29, the FAA Advisory Circular that supports for FAR-29 and CS-29 in 1999, following work by a JAA/FAA/Industry working group.  One would hope that AMC-29.1465 is considered as part of that review as the RVHMWG work was originally intended to revise MG15.

The FAA presentation is downloadable as part of a large zip file for the whole symposium or directly here 4.4._Shaw_Miscellaneous Systems & Equipment topics.

Aerossurance is an Aberdeen based aviation consultancy.  For practical advice and support you can trust on HUMS and VHM, all aspects of helicopter airworthiness and regulation, contact us at: enquiries@aerossurance.com

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