On October 27, the FAA released a new Special Airworthiness Information Bulletin--SAIB CE-06-05--warning mechanics to inspect and replace pre-1978 NAS-649 turnbuckles. The turnbuckles, which are used on aircraft flight control cables, are cracking in the barrel area, in turnbuckles with and without the V-notches used to secure quick safety clips.

The number of NAS-649 turn-buckle barrels remaining in the field is unknown, with a large number of them produced and unknown quantity that have been removed from service due to repairs, salvaged airframes, etc.

There is a replacement that should be used, the MS21251M turnbuckle, according to the SAIB. The specification for the MS21251 states that "a turnbuckle with a manufacturing date of 1978 or older shall not be used for replacement repairs since stress relieving was not required prior to this date."

The SAIB recommends that mechanics inspect aircraft for any pre-1978 turnbuckles and replace all turnbuckles stamped with a manufacturing date of 1978 or before, including pre-1978 MS21251M turnbuckles. Any spare pre-1978 turnbuckles should not be used. The turnbuckle barrels in question were identified with a manufacturing date on the barrel itself. Two of the turnbuckles that were identified by the safety recommendation had manufacturer dates on them and one did not, according to the FAA.

An excellent photo of a turnbuckle barrel crack is available on the FAA's Fairbanks, Alaska FSDO website at: http://www.alaska.faa.gov/faifsdo/maintturnbuckel.htm and is shown below. "Currently," the Fairbanks webpage stated, "we have found three instances of turnbuckles on small Piper aircraft that have had cracks originating around the `V' notch at the location where a safety clip may be installed. The cracks run lengthwise on the buckle from the `V' notch."

The cracks are about 5/8 to 3/4 of an inch long. The cracks have all been on NAS-649 series turnbuckles. The latest turnbuckle has a manufacturer stamp date on it of 1973.

While the FAA does not know how many of these turnbuckles remain in the field, "it is safe to say," an FAA engineer responded, "that there are a very large number of these type of turnbuckle barrels still in active service."

The turnbuckles should be identified with a manufacturing date on the barrel, he noted. "Turnbuckles should be inspected regularly during 100-hour and/or annual inspections for condition, security, and safetying." SAIB CE-06-05 is available at: http://www.faa.gov/aircraft/safety/alerts/saib/media/CE-06-05.pdf