# AD 74-06-02: AVCON Mufflers - Type: Airworthiness directive - Status: Current - Products: Lycoming 150 and160 hp Model O-320-( ) engine (Williams Robert or Barbara STC SA750CE or 3 others) - Effective: March 18, 1974 - Published: March 13, 1974 - Issued: March 1, 1974 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Small airplane - Amendment: 39-1798 - Registered aircraft: 35,940 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/5E9682BCE2C44C88862569990050FE97.0001 - DRS record last changed: November 21, 2025 - Page: https://openairdocs.org/ad/74-06-02 ## The airworthiness directive 74-06-02 CESSNA AND PIPER: Amendment 39-1798. Applies to Cessna Models 150, 170, 172 and 175 and Piper Model PA-28-140 airplanes modified in accordance with STCs SA750CE, SA806CE, SA807CE, SA777CE or SA 793CE respectively utilizing Avcon Industries, Inc., kits incorporating defective mufflers. Compliance: Required as indicated, unless already accomplished. To prevent possible leakage of carbon monoxide into the cabin heater system, accomplish the following: A) Prior to further flight, except that the aircraft may be flown in accordance with FAR 21.197 to a base where the inspection may be performed provided that the cabin heater system is in the "Off" position and the cabin fresh air vents are open, and at repetitive intervals not to exceed 5 hours' time in service thereafter, inspect the muffler inner shroud as follows: 1) Remove muffler outer shroud assembly. 2) Visually inspect the inner shroud flare and tail pipe weld area for evidence of cracks orleakage. If cracks or leaks are found, replace the muffler prior to further flight with a serviceable unit. 3) If no cracks or leakage are found during the inspection, safety wire the cabin heat control in the "Off" position. B) Within the next 25 hours' time in service after the effective date of this AD, replace the existing muffler with a serviceable unit, at which time compliance with Paragraph A is no longer required. C) Any alternate method of compliance with this AD must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region. Avcon Industries Service Letter No. 1, dated February 19, 1974, pertains to this subject matter. NOTE: The defective mufflers are contained in Avcon Kits of the following serial numbers: 556, 557, 562, 565, 580, 583, 584, 585, 588, 589, 591, 596, 597, 598, 599, 603, 604, 605, 608, 612, 618, 621, 623, 624, 627, 628, 632, 640, 642, 643, 644, 649, 650, 656, 659, 668, 669, 674 and 690. Confirmation ofaffected aircraft can be obtained by comparing the Avcon serial number stamped on the STC Kit I.D. tag with the Avcon serial number noted above. STC Kit I.D. tags are mounted near the aircraft manufacturer's I.D. tag. This amendment becomes effective March 18, 1974, to all persons except those to whom it was made effective by letter dated February 22, 1974. ## Affected data sheets (5) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS 3A12](https://openairdocs.org/tcds/3A12): Textron Aviation Inc.; names 18 of 18 models: 172F (USAF T-41A), 172M, 172Q, 172R, 172K, 172G, 172A, 172L… - [TCDS 3A19](https://openairdocs.org/tcds/3A19): Textron Aviation Inc.; names 13 of 18 models: 150L, 150B, 150D, 150E, 150M, 150K, 150C, 150G… - [TCDS 3A17](https://openairdocs.org/tcds/3A17): Textron Aviation Inc.; names 5 of 12 models: 172RG, 175, 175B, 175C, 175A - [TCDS A-799](https://openairdocs.org/tcds/A-799): Textron Aviation Inc.; names 3 of 3 models: 170, 170A, 170B - [TCDS 2A13](https://openairdocs.org/tcds/2A13): Piper Aircraft Inc.; names 1 of 18 models: PA-28-140 ## 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: 35,940 (35,940 by airframe model, 0 by engine model) - Makers: Cessna 30,439, Piper 4,258, Textron 1,239, P Z L Koliber 4 Models with the most aircraft: - [Piper PA-28-140](https://openairdocs.org/model/piper-pa-28-140): 4,258 aircraft (airframe model) - [Cessna 172M](https://openairdocs.org/model/cessna-172m): 3,573 aircraft (airframe model) - [Cessna 172N](https://openairdocs.org/model/cessna-172n): 3,138 aircraft (airframe model) - [Cessna 172S](https://openairdocs.org/model/cessna-172s): 1,915 aircraft (airframe model) - [Cessna 172](https://openairdocs.org/model/cessna-172): 1,805 aircraft (airframe model) - [Cessna 150L](https://openairdocs.org/model/cessna-150l): 1,447 aircraft (airframe model) - [Cessna 150M](https://openairdocs.org/model/cessna-150m): 1,439 aircraft (airframe model) - [Cessna 170B](https://openairdocs.org/model/cessna-170b): 1,300 aircraft (airframe model) - [Textron 172S](https://openairdocs.org/model/textron-172s): 1,239 aircraft (airframe model) - [Cessna 172P](https://openairdocs.org/model/cessna-172p): 1,111 aircraft (airframe model) - [Cessna 150F](https://openairdocs.org/model/cessna-150f): 1,063 aircraft (airframe model) - [Cessna 172K](https://openairdocs.org/model/cessna-172k): 1,026 aircraft (airframe model) - [Cessna 150G](https://openairdocs.org/model/cessna-150g): 977 aircraft (airframe model) - [Cessna 172L](https://openairdocs.org/model/cessna-172l): 857 aircraft (airframe model) - [Cessna 172H](https://openairdocs.org/model/cessna-172h): 780 aircraft (airframe model) - [Cessna 150H](https://openairdocs.org/model/cessna-150h): 756 aircraft (airframe model) - [Cessna 172G](https://openairdocs.org/model/cessna-172g): 722 aircraft (airframe model) - [Cessna 172F](https://openairdocs.org/model/cessna-172f): 717 aircraft (airframe model) - [Cessna 172R](https://openairdocs.org/model/cessna-172r): 683 aircraft (airframe model) - [Cessna 150J](https://openairdocs.org/model/cessna-150j): 659 aircraft (airframe model) All 44 models: https://openairdocs.org/ad/74-06-02/models.md Every aircraft: https://openairdocs.org/ad/74-06-02/aircraft.md ## Related documents - [STC SA750CE](https://openairdocs.org/stc/SA750CE): Installation of Lycoming 150 and160 hp Model O-320-( ) engine. (150, 150A, 150C, 150D, 150E, 150F, 150K, 150J, A150K, 150L, A150L, 150B, 150M, 150H, 150G LANDPLANES). Williams Robert or Barbara, Named in the applicability - [STC SA777CE](https://openairdocs.org/stc/SA777CE): Installation of Lycoming 180 hp engine and a Hartzell HC-C2YK-1A/766A-2 propeller.. Robert L & Barbara V Willia,s, Named in the applicability - [STC SA806CE](https://openairdocs.org/stc/SA806CE): Installation of Lycoming engine model O-360-( ) and propellers.. Williams Robert or Barbara, Named in the applicability - [STC SA807CE](https://openairdocs.org/stc/SA807CE): Installation of Lycoming 180 hp engine and constant speed propeller. (172P LANDPLANES). Robert or Barbara Williams, Named in the applicability --- 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.