# AD 73-13-08: Turbochargers

- Type: Airworthiness directive
- Status: Current
- Products: Cessna 421B
- Effective: June 27, 1973
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Small airplane
- Amendment: 39-1674
- Registered aircraft: 225 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/CF4D65C507F2BE0C86256A34006422C5.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/73-13-08

## The airworthiness directive

73-13-08 CESSNA: Amdt. 39-1674. Applies to Model 421B (Serial Numbers 421B0260 through 421B0346) airplanes having AiResearch TH0871 turbochargers with serial number prefixes BC or later installed and to any Model 421B airplane prior to Serial Number 421B0260 on which new turbochargers with serial number prefixes BC and later or remanufactured turbochargers with serial number prefixes BCR and later have been installed.

NOTE: Re turbochargers, the first letter B indicates the year of manufacture, i.e., 1972. The second letter C, D, E, etc., indicates the month of manufacture. Therefore, prefix BD is later than BC, BE is later than BD, etc. An R following the dating letters indicates the unit has been remanufactured. Turbochargers affected are those manufactured or remanufactured subsequent to July 1, 1972.

Compliance: Required as indicated, unless already accomplished.

To prevent loss of engine oil, within the next 25 hours' time in service after the effective date of this AD, install a check valve in the crankcase breather oil separator line in accordance with instructions set forth in Cessna Service Letter No. ME73-10, dated May 18, 1973, or later FAA-approved revision, or any equivalent modification approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.

This amendment becomes effective June 27, 1973.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A7CE](https://openairdocs.org/tcds/A7CE): Textron Aviation Inc.; names 1 of 16 models: 421B

## 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: 225 (225 by airframe model, 0 by engine model)
- Makers: Cessna 225

Models with the most aircraft:

- [Cessna 421B](https://openairdocs.org/model/cessna-421b): 225 aircraft (airframe model)

All 1 models: https://openairdocs.org/ad/73-13-08/models.md
Every aircraft: https://openairdocs.org/ad/73-13-08/aircraft.md

Its text cites no advisory circulars or STCs.

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