Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
SW-09-30
May 27, 2009
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin alerts you, owners and
operators of Enstrom Helicopter Corporation (Enstrom) Models F28F,
280F, and 280FX helicopters, of an airworthiness concern with the
engine pylon in the area adjacent to the belt tensioning assembly
mounting bracket.
Background
On May 31, 2001, Enstrom issued Service Information Letter (SIL) No.
0152, after receiving a report of a broken pylon in the area adjacent
to the belt tensioning assembly mounting bracket. At that time,
Enstrom’s records indicated three other failures in a ten year time
period. Also, the failures were considered not a chronic problem,
resulting from either a rough belt or improperly adjusted belt tension
and idler pulley. The SIL recommended an inspection of the pylon
adjacent to the belt tensioning assembly mounting bracket and
maintenance procedures for adjusting the belt tension assembly,
“snubber roller”, and idler pulley.
Recently, Enstrom received reports of three cracked pylons in the same
area addressed by SIL No. 0152. One occurred in flight and the pilot
noted a high vibration and loud noise. The pilot made an emergency
landing and found a cracked tube in the pylon. The crack was in the
area adjacent to the belt tensioning assembly mounting bracket. During
their 50 hour periodic inspection, two other helicopters were found to
have cracks in this same area. As a result of these reports, Enstrom
issued Service Directive Bulletin No. 0108, dated April 16, 2009.
At this time, the airworthiness concern is not an unsafe condition that
would warrant airworthiness directive (AD) action under Title 14 of the
Code of Federal Aviation Regulations (14 CFR) part 39. Even though the
cracked pylon tube may cause an increase in pilot workload, the FAA and
Enstrom do not believe that this would overstress the structure and
would not result in the loss of the aircraft.
Recommendations
We recommend you review Enstrom SIL No. 0512, dated May 31, 2001, and
conduct the inspections called out in Enstrom Service Directive
Bulletin No. 0108, dated April 16, 2009. If damage is found, contact
Enstrom Customer Service for repair instructions.
For Further Information Contact
Gregory J. Michalik, Enstrom Helicopter Program Manager, FAA Chicago
Aircraft Certification Office, 2300 East Devon, Des Plaines, IL 60018;
phone: (847) 294-7135; email: gregory.michalik@faa.gov