Important bulletin for Lycoming engines

Lycoming’s 540 Series six-cylinder engine, one of the types affected. Image © Lycoming

CASA is keen to ensure all operators of aircraft with Lycoming engines are aware of Airworthiness Bulletin 85-020 Issue 3 – 14, of August 2017. It refers to a problem which can cause the engines to fail in flight, and which has happened at least five times.

A recent US Federal Aviation Administration urgent airworthiness directive requires some of these engines to be inspected and repaired within 10 hours.

AWB 85-020 applies to two groups of Lycoming engines:

Group one –

  • All Lycoming reciprocating aircraft engines which were new, factory rebuilt or factory overhauled during the 2011 calendar year.

Group two –

  • Lycoming reciprocating aircraft engines with a serial number listed in Table 1 of Lycoming Service Bulletin (SB) No. 632B.
  • Lycoming reciprocating aircraft engines repaired or overhauled using connecting rod assemblies or connecting rod bushing identified in Table 2 of Lycoming SB No. 632B.

Defective bushings in group one engines have been linked to ‘events’ involving O-360, O-540 or IO-540 series engines installed in Robinson R22 and R44 helicopters, and GippsAero GA8 aircraft. There have been five uncontained engine failures reported worldwide with one uncontained failure reported by an Australian operator on an IO-540-E1B5 Engine.

In brief, the problem is that small-end connecting rod bushes have become loose and worn excessively, becoming shorter in service. This greatly increases wear on the connecting rods, causing engine failure in some cases.

The cause of the bush problem is unknown for group one engines, and linked to batches of undersized bushes for group two engines. Group two engines deteriorate more than group one engines. Extreme wear of bushes has been discovered in engines with about 1000 hours in service

The bulletin details what owners and operators need to do to correct the problem and maintain airworthiness.

For group one engines:

  • At each engine oil change – change the oil and filter and carry out inspection per the provisions of Lycoming SB 480F
  • Visually inspect the condition and check the security of little end connecting rod bushes in accordance with Lycoming SB 630A.

For group two engines:

  • Perform inspection requirements and take corrective actions in accordance with FAA Airworthiness Directive (AD) 2017-16-11.
  • This will require compliance with the service information given in Lycoming SB No. 632B, within 10 operating hours from 15 August 2017.

Obviously, any unusual indication or behaviour by an engine covered in AWB 85-20 should be investigated at once, even if it is well within the compliance period.


  1. Please re read the bulletin. Group 1 engines have the exact same bushing as Group II – so both groups need to be inspected within 10 hrs.
    Lycoming Engines.

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