# SAIB 2026-18: NOSE/TAIL LANDING GEAR, Installation of AeroControlex STC ST01255CH may allow water to leak and freeze on the nose wheel steering cables and prevent pilot from steering - Type: Special airworthiness information bulletin (advisory, not mandatory) - Status: Current - Revision: 0 - Issued: October 23, 2026 - Products: Boeing 737-100 Series, 737-200 Series, 737-300 Series, 737-400 Series and 737-500 Series - Product type: Aircraft, Large Airplane - PDF: https://openairdocs.org/files/sha256/07/08/07087ec69be89e1ea9b42052f4fb4223436aa08c8ed02327b50a68f6f12bfbab - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID171655642820261024005012.0001 - DRS record last changed: October 24, 2026 - Page: https://openairdocs.org/saib/2026-18 ## Text FAA Aviation Safety **SPECIAL AIRWORTHINESS** INFORMATION BULLETIN SUBJ: NOSE/TAIL LANDING GEAR, Installation of AeroControlex STC ST01255CH may allow water to leak and freeze on the nose wheel steering cables and prevent pilot from steering. SAIB: 2026-18 Date: October 23, 2026 This is information only. Recommendations aren’t mandatory. Introduction This Special Airworthiness Information Bulletin advises owners and operators of The Boeing Company Model 737-100, -200, -300, -400 , and -500 Series airplanes equipped with AeroControlex Supplemental Type Certificate (STC) ST01255CH of the potential for water to leak from the connection of the potable water drain line at the outboard forward lavatory wall and lead to the accumulation of ice on the nose wheel steering cables. 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 Boeing Model 737-500 airplane reported that the nose wheel steering (NWS) was not responsive during landing and roll. The pilot was able to use additional force on the NWS control and the NWS returned to normal operation. Maintenance performed an inspection and found ice had accumulated on the NWS cables. This ice formation was attributed to a water leak from the outboard connection of the forward lavatory potable water drain line. This potable water drain line had been previously modified by the installation of AeroControlex STC ST01255CH as part of an alternate means of compliance to FAA AD 99-01-16 (64 FR 1112, January 8, 1999) . The AeroControlex STC installs an isolator drain valve which may allow the potable water drain line to become pressurized if the forward lavatory selector valve is set to drain or internally leaks during flight. Installation of this drain valve reuses the original drain line and clamp to the outboard lavatory wall, which are not pressure-rated components. This potable water drain line is intended to be empty during flight as the forward lavatory selector valve should be set to “OFF or SUPPLY” when the aircraft is returned to service as indicated by the lavatory placard installed by this STC. Setting the forward lavatory selector valve to “DRAIN” may lead to pressurization of the potable water drain line. Should the potable water drain line pressurize, water may leak from the connection at the outboard forward lavatory wall with the potential to accumulate and form ice on the NWS cables, which may prevent normal NWS operation. Recommendations The FAA recommends that owners and operators ensure the outboard lavatory potable water drain line connection is securely clamped in place if water is leaking or accumulating near the nose wheel steering cables, beneath the lavatory, or following maintenance. Follow the post-installation system checkout procedures found in AeroControlex STC Installation Manual 80-0106, Section 8.0. to prevent leaks should the potable water line become pressurized. For Further Information Contact Olivia Rasmussen, Aviation Safety Engineer, 2300 E Devon Ave, Des Plaines, IL 60018, United States; phone: (847) 294-7117; e-mail: Olivia.E.Rasmussen@faa.gov. ## Registered aircraft it may concern (OpenAirDocs) Registry models matched by make and model, the same way as ADs, most registered aircraft first. - [Boeing 737-400](https://openairdocs.org/model/boeing-737-400): 8 registered aircraft (airframe model) - [Boeing 737-436](https://openairdocs.org/model/boeing-737-436): 6 registered aircraft (airframe model) - [Boeing 737-500](https://openairdocs.org/model/boeing-737-500): 6 registered aircraft (airframe model) - [Boeing 737-300](https://openairdocs.org/model/boeing-737-300): 4 registered aircraft (airframe model) - [Boeing 737-205](https://openairdocs.org/model/boeing-737-205): 3 registered aircraft (airframe model) - [Boeing 737-484](https://openairdocs.org/model/boeing-737-484): 3 registered aircraft (airframe model) - [Boeing 737-490](https://openairdocs.org/model/boeing-737-490): 3 registered aircraft (airframe model) - [Boeing 737-524](https://openairdocs.org/model/boeing-737-524): 3 registered aircraft (airframe model) - [Boeing 737-505](https://openairdocs.org/model/boeing-737-505): 2 registered aircraft (airframe model) - [Boeing 737-200](https://openairdocs.org/model/boeing-737-200): 1 registered aircraft (airframe model) - [Boeing 737-201](https://openairdocs.org/model/boeing-737-201): 1 registered aircraft (airframe model) - [Boeing 737-209](https://openairdocs.org/model/boeing-737-209): 1 registered aircraft (airframe model) - [Boeing 737-301](https://openairdocs.org/model/boeing-737-301): 1 registered aircraft (airframe model) - [Boeing 737-306](https://openairdocs.org/model/boeing-737-306): 1 registered aircraft (airframe model) - [Boeing 737-319](https://openairdocs.org/model/boeing-737-319): 1 registered aircraft (airframe model) - [Boeing 737-330](https://openairdocs.org/model/boeing-737-330): 1 registered aircraft (airframe model) - [Boeing 737-401](https://openairdocs.org/model/boeing-737-401): 1 registered aircraft (airframe model) - [Boeing 737-405](https://openairdocs.org/model/boeing-737-405): 1 registered aircraft (airframe model) - [Boeing 737-528](https://openairdocs.org/model/boeing-737-528): 1 registered aircraft (airframe model) - [Boeing 737-112](https://openairdocs.org/model/boeing-737-112): 0 registered aircraft (airframe model) - [Boeing 737-130](https://openairdocs.org/model/boeing-737-130): 0 registered aircraft (airframe model) - [Boeing 737-204](https://openairdocs.org/model/boeing-737-204): 0 registered aircraft (airframe model) - [Boeing 737-212](https://openairdocs.org/model/boeing-737-212): 0 registered aircraft (airframe model) - [Boeing 737-214](https://openairdocs.org/model/boeing-737-214): 0 registered aircraft (airframe model) - [Boeing 737-217](https://openairdocs.org/model/boeing-737-217): 0 registered aircraft (airframe model) - [Boeing 737-219](https://openairdocs.org/model/boeing-737-219): 0 registered aircraft (airframe model) - [Boeing 737-222](https://openairdocs.org/model/boeing-737-222): 0 registered aircraft (airframe model) - [Boeing 737-228](https://openairdocs.org/model/boeing-737-228): 0 registered aircraft (airframe model) - [Boeing 737-229](https://openairdocs.org/model/boeing-737-229): 0 registered aircraft (airframe model) - [Boeing 737-230](https://openairdocs.org/model/boeing-737-230): 0 registered aircraft (airframe model) - [Boeing 737-232](https://openairdocs.org/model/boeing-737-232): 0 registered aircraft (airframe model) - [Boeing 737-236](https://openairdocs.org/model/boeing-737-236): 0 registered aircraft (airframe model) - [Boeing 737-241](https://openairdocs.org/model/boeing-737-241): 0 registered aircraft (airframe model) - [Boeing 737-242](https://openairdocs.org/model/boeing-737-242): 0 registered aircraft (airframe model) - [Boeing 737-244](https://openairdocs.org/model/boeing-737-244): 0 registered aircraft (airframe model) - [Boeing 737-247](https://openairdocs.org/model/boeing-737-247): 0 registered aircraft (airframe model) - [Boeing 737-248](https://openairdocs.org/model/boeing-737-248): 0 registered aircraft (airframe model) - [Boeing 737-258](https://openairdocs.org/model/boeing-737-258): 0 registered aircraft (airframe model) - [Boeing 737-260](https://openairdocs.org/model/boeing-737-260): 0 registered aircraft (airframe model) - [Boeing 737-266](https://openairdocs.org/model/boeing-737-266): 0 registered aircraft (airframe model) - [Boeing 737-268](https://openairdocs.org/model/boeing-737-268): 0 registered aircraft (airframe model) - [Boeing 737-269](https://openairdocs.org/model/boeing-737-269): 0 registered aircraft (airframe model) - [Boeing 737-275](https://openairdocs.org/model/boeing-737-275): 0 registered aircraft (airframe model) - [Boeing 737-277](https://openairdocs.org/model/boeing-737-277): 0 registered aircraft (airframe model) - [Boeing 737-281](https://openairdocs.org/model/boeing-737-281): 0 registered aircraft (airframe model) - [Boeing 737-282](https://openairdocs.org/model/boeing-737-282): 0 registered aircraft (airframe model) - [Boeing 737-284](https://openairdocs.org/model/boeing-737-284): 0 registered aircraft (airframe model) - [Boeing 737-286](https://openairdocs.org/model/boeing-737-286): 0 registered aircraft (airframe model) - [Boeing 737-287](https://openairdocs.org/model/boeing-737-287): 0 registered aircraft (airframe model) - [Boeing 737-291](https://openairdocs.org/model/boeing-737-291): 0 registered aircraft (airframe model) All 80: https://openairdocs.org/saib/2026-18/models.md --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.