Mode Aviation
Reference No. R201300011
Date reported 12 February 2013
Concern title Light sport aircraft engine design flaw
Concern summary

The concern related to the design of a light sport aircraft engine with the reporter advising that the engine rarely makes it to 1,000 hours without major mechanical problems developing.

Industry / Operation affected Aviation: General aviation
Concern subject type Aviation: Maintenance

Reporter's concern

The reported expressed a safety concern regarding the safety of a light sport aircraft engine.

The reporter stated that the engine rarely makes it to 1,000 hours without a major mechanical problem developing (for example excessive ring wear, fretting of engine crankcases, flywheel bolts shearing, and excessive CHT temperatures). The reporter has stated that there is a design flaw with the engine - the piston alignment is incorrect and this is manifesting in reliability issues. The operator has produced fixes for several of the resulting issues but these have not addressed the cause of the problem.

Operator's response (Operator 1)

It is important to have good maintenance of an engine for it to reach 1,000 and 2,000 hours. Adherence to service bulletins is also important. We run maintenance workshops several times a year for L2 and LAMEs to educate maintainers regarding the intricacies of the engines. We highly recommend that maintainers who intend to work on the engines undertake this training. Even the most experience aircraft maintainers have benefited from this training. We have a constant development program advancing the engine design.

Regulator's response (Regulator 1)

CASA has reviewed the REPCON and is aware of claims that the particular light sport aircraft engine is incorrectly designed. While there may be some argument to support the reporter's claims, without all design data and operating parameters, it is not possible to simply overlay this contention to the product.

CASA will discuss the issue raised in the REPCON with the engine manufacturer as part of the current consultation CASA is undertaking with them.

Regarding the reliability of the engine more generally, a search of the Australian civil aircraft register (VH- ) has identified 129 aircraft using the engines. Approximately half of these aircraft are on 'Experimental Certificates' with most of the others on 'Special Certificate of Approval (CofA) - Light Sport Aircraft (LSA) or Primary Category'. Using CASA's service difficulty report database, in relation to the engine defects from 1 January 2007 to the present, the following has been identified:

  • A total of 75 defects (89 defects were recorded of which 14 were incorrectly categorised).
  • Out of the 75 defects, five related to civil (VH) registered aircraft.
  • Three defects were recorded against [type 1] aircraft, which are the only 'Type Certified' aircraft under TC: VA515.
    25 defects were recorded against [type 2] aircraft, which is a Factory-built LSA model, eligible for Special CofA - LSA.
  • 42 (the majority) of the defects involved RA-Aus registered aircraft, with most of those involved having a 'Special CofA - LSA'.

The remaining aircraft were on an Experimental Certificate. Importantly, it should be noted that under the terms of existing LSA legislation, all 'Continuing Airworthiness Instructions' from the manufacturer are mandatory. No modification/design changes are permitted without the manufacturer's approval, not even CASR subpart 21M approval.

ATSB comment

As a result of this report and an increase in the number of notifications the ATSB received regarding engine problems in light sport aircraft, the ATSB has commenced a research investigation into the reliability of light sport aeroplane engines.

Last update 11 March 2016