# AD 47-47-05: Stewart-Warner 921B Heaters

- Type: Airworthiness directive
- Status: Current
- Products: Martin-Marietta 202
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/2BB9043519E9F05A8625698A0073084C.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/47-47-05

## The airworthiness directive

47-47-05 MARTIN: (Was Service Note 1 of AD-795-1.) Applies to Model 202 Aircraft.

The Stewart-Warner 921-B heaters in the Cabin heating and wing thermal deicing systems shall be inspected in accordance with the following: Any heaters indicating impending failure as a result of these inspections shall be replaced immediately:

1. Inspect combustion chamber and heat exchanger end plates on each end of the cabin heaters for signs of cracks at each 30 hours of airplane operation. For wing heaters this inspection should be conducted at each 60 hours of airplane operation.

2. Remove cabin heater for complete inspection and pressure test every 300 hours of airplane operation. In the case of wing heaters this inspection should be conducted at not less than every 600 hours of airplane operation.

3. Item 2. is to be repeated every 100 hours of airplane operation after the first 300- hour inspection for cabin heaters and every 200 hours of operation after the first 600-hourinspection in the case of wing heaters.

NOTE: The above inspection periods may be varied within reasonable limits to suit the normal inspection periods of scheduled air carrier operators at the discretion of the assigned CAA Maintenance Inspector. If heater operating time is logged separately from airplane operating time, the inspections specified in 2. and 3. may be conducted on the basis of heater operating time except that, if this is done, both wing and cabin heaters should be inspected after the first 300 hours and each 100 hours thereafter.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A-795](https://openairdocs.org/tcds/A-795): Martin-Marietta Corporation; names 1 of 2 models: 202

## Registered aircraft it may apply to (OpenAirDocs)

No registered aircraft matched the models it names.

Its text cites no advisory circulars or STCs.

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