FAA SPECIAL AIRWORTHINESS
Aviation Safety INFORMATION BULLETIN
SAIB: NM-16-21
SUBJ: Flight Controls Date: August 8, 2016
This is information only. Recommendations aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) advises owners and operators of The
Boeing Company Model 737-600/-700/-700C/-800/-900/-900ER airplanes of procedural
changes for horizontal stabilizer position settings during de-icing.
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.
Background
An operator of a Model 737-800 airplane reported an uncommanded pitch-up event after intercepting
the glide slope during a normal approach. The elevator failed to properly respond to autopilot
commands, and the flight crew reported that the elevator responded only after higher column forces
were applied. It was determined that de-icing fluid can enter the tail cone during airplane de-icing
with the horizontal stabilizer trimmed to the full leading-edge-up position. This fluid can then freeze
around the elevator power control unit (PCU) input levers, restricting their movement. Boeing testing
has shown that positioning the horizontal stabilizer in the green band range during de-icing will
reduce the amount of fluid that can enter the tail cone through the elevator linkage side cutout.
Procedural changes have been made to the 737 Flight Crew Operations Manual (FCOM)
D6-27370-TBC, dated September 25, 2014, and the Boeing 737-600/700/800/900 Aircraft
Maintenance Manual (AMM), Task 12-33-01 “Cold Weather Maintenance Procedure,” dated
October 15, 2014, to reduce the amount of fluid that can enter the tail cone through the elevator
linkage side cutout. The revised FCOM procedure instructs the flight crew to position the horizontal
stabilizer at the calculated take-off setting within the green band range for de-icing. The revised
AMM procedure instructs maintenance personnel to position the horizontal stabilizer to five units of
trim. Additional guidance for these procedures can be found in Boeing Fleet Team Digest
737NG-FTD-27-13005.
Recommendations
The FAA recommends that flight crews and maintenance technicians of the referenced airplanes
follow the procedures outlined in the above service information.
For Further Information Contact
Kelly McGuckin, Aerospace Engineer, Mechanical/Flight Controls Branch, ANM-130S, FAA,
Seattle Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington
98057-3356; telephone 425-917-6490; fax 425-917-6590; e-mail
[email protected].
1
For Related Service Information Contact:
Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65,
Seattle, Washington 98124-2207; telephone 206-544-5000, extension 1; fax 206-766-5680; Internet
https://www.myboeingfleet.com.
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Please find attached a Foreign State of Design Advisory document, endorsed by EASA.
This advisory document is also online at https://ad.easa.europa.eu/ad/NM-16-21 .
Should you have any questions, please contact the Agency by e-mail at
[email protected] or by fax,
No.: +49 221 89990 9515.
Safety Information Section Email:
[email protected]
EASA Website
(Attachment is in Acrobat PDF format)
Postal: Postfach 10 12 53, 50452 Cologne, Germany
An agency of the European Union
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