An AD will soon be released based on MT Propeller Service Bulletin No.30 R7, which was first issued in November 2014. The subject of the bulletin is “Replacement of Blade Lag Screws of a certain production lot.”
With a recent incident on June 19, 2022, in which a Great Lakes 2T-1A-2 experienced a blade loss, Gerd Muehlbauer, President of MT Propeller Entwicklung GmbH, is requesting an AD from the EASA who will then forward it to the FAA.
“At the time of the original bulletin in 2014, we assumed that an Alert Service Bulletin was enough to inform our customers and Service Centers about the need of replacement of lag screws in certain blade of different propellers according to the listing in the SB”, said Gerd. “After seven years we are now finding that a great number of affected blades have not been replaced or modified. Until the AD comes out, we would like to bring this alert to our flying community as soon as possible.”
The reason for a possible fatigue failure of the Lag Screw is a manufacturing flaw in the transition area from the thread to the shaft, which was only detected after a routine test of a particular batch, which we perform frequently. Again, this was more than 7 years ago.
The propellers in such airplanes could be the 2-blade MTV-15-B-C, the 3-blade MTV-9-B-C and the 4-blade MTV-14-B-C. Most of these propellers may start with Serial-Numbers 13XXXX and 14XXXX and a few from earlier years according to the SB. 15XXXX and higher or 12XXXX and lower are not affected, but see the SB.
The blades should immediately be inspected according to Owners Manual No. E-124, Section 6, Item 6.2.2.4 - if the silicone sealer is cracked, stop flying right now because this is the indication that the blade is already moving in the ferrule.
The SB no. 30 R7 covers action that aircraft owners and their mechanics must take to replace the lag screws in question. https://www.mt-propeller.com/pdf/sbs/sb30r7.pdf
Further information can be obtained by contacting MT Propeller support at: techsupport@mt-propeller.com .
