Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
July 22, 2016
This is information only. Recommendations
This Special Airworthiness Information Bulletin (SAIB) alerts you,
owners, operators, and certificated repair or maintenance facilities of
airplanes equipped with Honeywell Inc. (Honeywell) TPE331-10 and
TPE331-11 series turboprop engines, to 1st stage turbine blade failures.
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 Regulations (14 CFR) part 39.
We have received reports of 21 1st stage turbine blade failures on
Honeywell TPE331-10 and -11 series engines from October, 1997 to
November, 2013. These failures caused 15 in-flight shutdown events
resulting in moderate to severe turbine damage. Of the 21 blade
failures, 9 involved 1st stage turbine nozzle distress and nozzle vane
burn-through. Nozzle vane burn-through creates a one-per-rev excitation
to the 1st stage turbine blades, which contributes to premature blade
The Accomplishment Instructions of Honeywell Service Bulletin (SB)
TPE331-73-0284, dated November 3, 2014, recommends a borescope
inspection (BSI), only after fuel nozzle distress, in accordance with
the engine maintenance manual (EMM). The TPE331-10 and -11 series EMM
instructions in Section 72-00-00, Inspection/Check, identify BSI
equipment that is not readily available or effective for this
application. Additionally, the EMM does not clearly define nozzle vane
burn-through. This SAIB supplements Honeywell SB TPE331-73-0284 by
providing additional guidance for BSI of the 1st stage turbine nozzle
vanes to prevent 1st stage turbine nozzle vane burnthrough and reduce
The FAA recommends a BSI at
every fuel nozzle inspection interval when the fuel nozzle manifold is
removed from the engine, not to exceed 450 hours since last inspection.
We also recommend BSI viewing through 4 fuel nozzle boss openings to obtain full inspection coverage of the 1st stage nozzle.
We also recommend using an RF Systems videoscope with a 3.9 mm or 6.9 mm flex insertion tube or equivalent.
The flex insertion tube must be
used with an appropriately sized guide tube as shown in Figure 1 below.
When selecting a flex insertion tube, it is important to note that
larger diameter tubes allow more light at the inspection site, but will
have less flexibility. Synflex guide tubing provides the strength and
flexibility of aluminum tubing and can be bent by hand. Some borescope
suppliers may provide properly-sized Synflex tubing.
ILLUSTRATION (Figure 1)
Figure 1. Cross-section of TPE331-11U Engine Power Section with Borescope Guide-Tube in Combustor
Figures 2 – 4 provide photos of TPE331 engine 1st stage turbine stator nozzle vanes with acceptable and unacceptable conditions.
Joseph Costa, Aerospace Engineer, FAA, Los Angeles Aircraft
Certification Office, 3960 Paramount Blvd., Suite 100, Lakewood, CA
90712; phone: 562-627-5246; fax: 562-627-5210; email:
For Related Service Information Contact
Honeywell International Inc., 111 S. 34th Street, Phoenix, AZ
85034-2802; phone: 800-601-3099; Internet: