Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
CE-09-28
May 12, 2009
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) informs you, a
registered owner or operator, of a Air Tractor Model AT-802 and AT-802A
airplane. The SAIB specifically informs you that the aft fuselage
diagonal tube, part number 11029-10, may crack on airplanes prior to
serial number -0259 when equipped with floats. The FAA has received
reports of cracked diagonal tubes only on float equipped airplanes.
At this time, this airworthiness concern is not considered an unsafe
condition that would warrant an airworthiness directive (AD) action
under Title 14 of the Code of Federal Regulations (14 CFR part 39).
Background
In August 2007, Air Tractor issued Snow Engineering Co. Service Letter
#266 to address cracks in AT-802 and AT-802A aft fuselage diagonal
tubes, part number 11029-10. The Service Letter provides for one-time
inspection for cracks, recurring inspection of the tube for float
equipped airplanes, a reporting requirement to the factory for any
cracks found, and a procedure to install a stronger tube as corrective
action to cracked tubes and termination of the inspections. The Service
Letter applies to AT-802 and AT-802A airplanes prior to serial number
-0259.
Since that time, Air Tractor has received further service information
supporting that the problem is isolated to float equipped AT-802 and
AT-802A airplanes only. No cracks were reported for nonfloat equipped
airplanes. To date, 40 affected AT-802 and AT-802A airplanes have been
modified with floats for operating on water. Air Tractor reports that
10 of those 40 airplanes have been found with the aft fuselage diagonal
tube cracked.
Air Tractor believes the cracks develop as a result of the high power
requirements associated with operating float equipped airplanes, and
from operation in rough waters. The factory installed stronger diagonal
tubes in production airplanes starting at serial number -0259 to
address this problem. The original tube material was 7/8” outside
diameter (OD) x .035” wall thickness (WT); the replacement tube is 7/8”
OD x .058” WT. Note that the part number was not changed. Operators
will need to confirm which tubes are installed by aircraft serial
number effectivity and review of the aircraft logbook for whether the
tube has already been replaced.
Recommendations
The FAA recommends that you inspect your float equipped AT-802 and
AT-802A airplanes prior to serial number -0259 that still have the
original .035” WT part number 11029-10 diagonal tube. You should
perform the initial inspection within the next 25 flight hours in
accordance with Snow Engineering Co. Service Letter #266, dated
8/22/07. If you have the .035 WT tube installed, we also recommend that
you repeat the inspection at every 100 flight hours and during the
annual inspection until the stronger .058” WT replacement tube is
installed.
Replace any cracked diagonal tube prior to continued flight with the
thicker .058” part number 11029-10 replacement tube. We also recommend,
if not already done, that you replace the original .035” WT tube with
the .058” WT tube by the next major maintenance interval to eliminate
the probability of cracking and need for further inspections. Failure
to detect and replace a cracked diagonal tube can result in a reduction
in structural safety margins.