- Published
- December 4, 1956
- Issued
- December 4, 1956
- Models
- 377, 377MG, 377SGT
- Data sheet
- TCDSA-812
- Registered aircraft
- 1 matched by model
- Product
- Aircraft · Large airplane
Unofficial copy of the text in the FAA’s Dynamic Regulatory System. The FAA’s own copy is the authoritative one. DRS record last changed November 21, 2025.
Copies of the files this page was built from, with their SHA-256. Retrieved October 18, 2026.
| File | Size | SHA-256 | Original |
|---|---|---|---|
| FAA DRS HTML | 19 KB | 55f93763…28589dd | FAA DRS (API key needed) |
On this page
The airworthiness directive
55-09-01 BOEING: Applies to all Model 377 aircraft with Hamilton Standard Propellers. To be accomplished as soon as practicable but not later than June 30, 1955. Loss of manual r.p.m. control can occur as a result of tripping of the fast-acting magnetic circuit breaker before the slow-acting fuse is blown on a faulted branch. Improved circuit protective coordination and resultant reliability in the manual control function should be provided by replacing the "Manual" 10-ampere magnetic circuit breaker with a 5-ampere thermal type breaker, and replacing the four 5-ampere fuses in the synchronizer unit with 2 ampere Slo-Blo fuses. (Hamilton Standard Service Bulletin No. 283 dated December 21, 1953, covers this same subject.)
Affected TCDS · 1
The type certificate data sheets for the models this AD names, matched by model and maker.
Registered aircraft · 1
Registered aircraft whose airframe or engine model this AD names. Matched by model only, so check each against the AD’s applicability.