# AD 56-27-02: Engine Mount Welds - Type: Airworthiness directive - Status: Current - Products: Hiller UH-12, UH-12A and UH-12B - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Rotorcraft - Registered aircraft: 57 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/3BCF3E5E93A7DA0A86256A38005F33D8.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/56-27-02 ## The airworthiness directive 56-27-02 HILLER: Applies to All UH-12, UH-12A and UH-12B Helicopters Including Spares. Compliance required as soon as possible but not later than February 28, 1957. Investigation has revealed that defective welds may exist at the clamp lugs on the four upper lord mount supports on P/N 63100-2 lower frame assembly (engine mount), or on mounts, P/N 63100-2M, modified in accordance with Hiller Service Bulletin No. 51. Failure of this weld has resulted in tilting of the rotor mast and loss of collective pitch control. The following one-time inspection is required on the above mounts to detect possible defective welds which must be reworked as indicated. 1. If the engine mount is cadmium plated, no inspection of the weld will be required, since these lower frame assemblies have been fabricated subsequent to the period of questionable weldments. 2. If the engine mount is not cadmium plated, remove the paint from all four lord mount supports in the area of the clamplugs and inspect for identification markings in or around the weld at the clamp lugs. If the weld is stamped with either a 7 or 8 or no stamp at all, it will be necessary to remove the mount from service until such time as the lugs can be removed and rewelded to CAM 18 standards. (Hiller Service Information Letter No. 111 covers this subject.) ## Affected data sheets (2) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS 6H1](https://openairdocs.org/tcds/6H1): Siam Hiller Holdings Inc.; names 2 of 2 models: UH-12, UH-12A - [TCDS 6H2](https://openairdocs.org/tcds/6H2): Siam Hiller Holdings Inc.; names 1 of 2 models: UH-12B ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 57 (57 by airframe model, 0 by engine model) - Makers: Hiller 53, Hiller-Heli-Cab 1, Hiller-Helicopter Rep SVC 1, Hiller-Tri-Plex Ind.Inc. 1, Hiller-Yehnert 1 Models with the most aircraft: - [Hiller UH-12B](https://openairdocs.org/model/hiller-uh-12b): 35 aircraft (airframe model) - [Hiller UH-12A](https://openairdocs.org/model/hiller-uh-12a): 16 aircraft (airframe model) - [Hiller UH-12](https://openairdocs.org/model/hiller-uh-12): 2 aircraft (airframe model) - [Hiller-Yehnert UH-12](https://openairdocs.org/model/hiller-yehnert-uh-12): 1 aircraft (airframe model) - [Hiller-Helicopter Rep SVC UH-12B](https://openairdocs.org/model/hiller-helicopter-rep-svc-uh-12b): 1 aircraft (airframe model) - [Hiller-Tri-Plex Ind.Inc. UH-12B](https://openairdocs.org/model/hiller-tri-plex-ind-inc-uh-12b): 1 aircraft (airframe model) - [Hiller-Heli-Cab UH-12B](https://openairdocs.org/model/hiller-heli-cab-uh-12b): 1 aircraft (airframe model) All 7 models: https://openairdocs.org/ad/56-27-02/models.md Every aircraft: https://openairdocs.org/ad/56-27-02/aircraft.md Its text cites no advisory circulars or STCs. ## NTSB investigations that cite this AD (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB ATL99LA131](https://openairdocs.org/ntsb/ATL99LA131), Sep 11, 1999: Hiller UH-12A (N212W), Satartia, MS, substantial damage. Probable cause: The pilot's failure to maintain control of the helicopter while on approach which resulted in the uncontrolled collision with the ground. A factor was the pilot's physiological condition. --- 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.