Lycoming Airworthines Directive. Have you had recent engine work done?

This AD addresses a problem with small-end connecting rod bushings (part number LW-13923) that were shipped by Lycoming to overhaul shops and mechanics between November 2015 and November 2016. It turns out that there was a quality assurance problem with these bushings, and some of them had an outside diameter that did not conform with specifications. These bushings are pressed into the small end of Lycoming connecting rod assemblies using a hydraulic press. If the bushings are too small in diameter, the press-fit isn’t secure and the bushings can migrate out of the connecting rod when in service. That’s exactly what seems to be happening to a relatively small percentage of these non-conforming bushings, and it’s what prompted Lycoming to issue its AD.

Connecting Rod Bearing part number.
This AD affects all Lycoming engines if you have recently done engine tear down or overhaul.

Rod Number

Lot and Serial numbers

Landing Gear – Problem solving

shuttle-valve-disassembled

Shuttle valve (one of the many photos stepping through the investigation)

One of the aims of LOBO OZ has always been to provide a place for sharing discussions and investigations which Lancair Owners and Builders have experienced. In the linked article, Fred Moreno and Chris Howden outline their method of problem solving a landing gear issue:

Lancair IV VH-YFM has over several years experienced failures to retract the main landing gear after takeoff. Sometimes two green lights would remain illuminated, sometimes only one. Incidents were intermittent and widely separated in time, but began to occur more frequently. In all cases, slowing the aircraft to below 120 knots and recycling the landing gear (select down, then up again) would raise both main landing gear and the trip could be completed.

For those who are interested, they have written in extensive detail about how they approached the whole process – complete with photo and diagrams – Lancair IV Main Landing Gear Investigation.

The article also illustrates how collaboration and discussion on the Lancair Mailing List assisted in the investigation process:

After another occurrence a request for ideas and insights was broadcast on Lancair Mail News which resulted in several notes that others have experienced the same difficulties. The finger of suspicion was pointed to the shuttle valve which could malfunction and block the escape of fluid from MLG cylinders when they move to the retract position. This would explain why both gear would stay extended, but not why one gear would stay extended (green light on) while the other did not (green light off).

diagram

This figure is extracted from the Lancair IV builder’s manual.

In such precision machines, the value of questioning, discussion and sharing of problems and their solutions cannot be underestimated, so we hope this ‘holiday weekend’ reading is valuable to you. Let us know if there is something you too could share.