# AD 68-05-01: Exhaust Mufflers - Type: Airworthiness directive - Status: Current - Products: FS 2001 J5A-80, J5A (Army L-4F), J5B (Army L-4G), J5C, PA-14, PA-12, PA-12S, J-3, J3C-40, J3C-50, J3C-50S, J3C-65S and 58 more - Effective: March 31, 1968 - Published: February 28, 1969 - Issued: February 18, 1969 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Small airplane - Amendment: 39-726 - Registered aircraft: 11,870 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/7D69E97F85048A6086256E0100546820.0001 - DRS record last changed: November 21, 2025 - Page: https://openairdocs.org/ad/68-05-01 ## The airworthiness directive 68-05-01 PIPER: Amdt. 39-726. Applies to Piper J3, J4, J5, PA-11, PA-12, PA-14, PA-15, PA-16, PA-17, PA-18, PA-19, PA-20, PA-22, and PA-24 type airplanes, except PA-24-400 and PA-24-260 aircraft serial numbers 24-4783, 24-4804 and subsequent. Compliance required as indicated. (a) For all airplanes except Models J3, J4, J5, PA-11 and those referenced in paragraphs (i) and (j), which have exhaust mufflers with 950 or more hours time in service on the effective date of this AD, comply with paragraph (e) within the next 50 hours time in service and thereafter at intervals not to exceed 50 hours time in service from the last inspection. (b) For all airplanes except Models J3, J4, J5, PA-11 and those referenced in paragraphs (i) and (j), which have exhaust mufflers with less than 950 hours time in service on the effective date of this AD, comply with paragraph (e) within the next 50 hours time in service, and thereafter at intervals not to exceed 100 hours time in service from the last inspection. After the exhaust muffler has accumulated 950 hours time in service, comply with the inspection requirements of paragraph (a). (c) For all Models J3, J4, J5, and PA-11 airplanes which have exhaust mufflers with 950 or more hours' time in service on the effective date of this AD, comply with paragraph (e) within the next 50 hours' time in service and thereafter at intervals not to exceed 50 hours time in service from the last inspection. (d) For all Models J3, J4, J5, and PA-11 airplanes which have exhaust mufflers with less than 950 hours' time in service on the effective date of this AD, comply with paragraph (e) prior to the accumulation of 1000 hours' time in service and thereafter at intervals not to exceed 50 hours' time in service. (e) Inspect in accordance with paragraph (f), and paragraph (g) if applicable, the engine exhaust muffler and shroud assembly (including the internal baffle tube and tail pipe), carburetor heat shroud and air duct, support braces, clamps and brackets, exhaust stacks and manifolds. Do not alter those mufflers incorporating an internal baffle tube to remove the tube without prior FAA approval. (Piper Service Letter No. 324B describes the critical areas.) (f) Remove muffler assembly, disconnect air ducts, stacks, and shrouds as necessary, and visually inspect exterior and interior surfaces with a probe light and mirror for signs of cracks, corrosion, burn-throughs, heat damage, collapsed stack, or weld separations. For carburetor type engines, special attention should be given to the exhaust stack under the carburetor heat shroud. Except during the initial inspection, the muffler need not be removed from the airplane, provided visual inspection with probe light and mirror is made through the muffler tail pipe outlet and one end of the muffler at the stack connection. (g) If the inspection specified in paragraph (f) shows that the exhaust stacks and internal baffle tube arein good condition, but there are areas inside the muffler which cannot be adequately inspected with a probe light and mirror, accomplish one of the following: (1) Accomplish a submerged pressure check of the muffler and exhaust stack at 10 psi air pressure. (2) Conduct a ground test using a carbon monoxide indicator by heading the airplane into the wind, warming the engine on the ground, advancing the throttle to full static r.p.m. with cabin heat valves open, and taking readings of the heated airstream inside the cabin at each outlet (including rear seat heat outlet, if installed). Appropriate sampling procedures applicable to the particular indicator must be followed. If carbon monoxide concentration exceeds .005 percent or if a dangerous reading is obtained on an indicator not calibrated in percentages, inspect in accordance with (f), and perform a submerged pressure check of the muffler and exhaust stack at 10 psi air pressure before further flight. (3) Close and secure cabin heat valves at the firewall until a complete muffler inspection in accordance with paragraph (f) is accomplished. (h) Replace or repair parts found to have the defects listed in paragraph (f) before further flight, and thereafter comply with the inspection requirements of paragraph (b) or (d), whichever is applicable. Make welding repairs in accordance with Advisory Circular AC 43.13-1 or an FAA-approved equivalent. Pressure-check mufflers and stacks that are repair-welded before reinstallation. (Care should be exercised when reinstalling the exhaust system components to prevent distortion or preloading of parts.) (i) The repetitive inspection of paragraph (a) and (b) may be discontinued when hollow muffler P/N 24506 or P/N 26385 is installed on Model PA-24 aircraft; and on Model PA-24-250 aircraft when installed in combination with muffler support Kit. No. 756775 (Service Letter No. 412A) or Kit No. 757058 (Service Letter No. 481) as applicable, or an equivalent modification approved by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region. (j) For applicable PA-24-260 airplanes, the repetitive inspections of paragraph (b) must be accomplished at 50 hour intervals in lieu of 100 hour intervals until a barrier device is installed in each muffler in accordance with Piper Service Letter No. 518 or an equivalent modification approved by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region. Upon installation of the barrier devices, the repetitive inspections of paragraph (a) and (b) may be discontinued. (Piper Service Letters Nos. 324B, 324C, 412A, 481 and 518 cover this same subject.) Effective March 31, 1968. Revised March 5, 1969. ## Affected data sheets (19) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS 1A2](https://openairdocs.org/tcds/1A2): Piper Aircraft Inc.; names 15 of 18 models: PA-18-105 (Special), PA-18S-105 (Special), PA-18-125 (Army L-21A), PA-19 (Army L-18C), PA-18S-135, PA-18AS-135, PA-18S, PA-18S-150… - [TCDS 1A6](https://openairdocs.org/tcds/1A6): Piper Aircraft Inc.; names 8 of 8 models: PA-22S-135, PA-22S-150, PA-22-108, PA-22-160, PA-22-150, PA-22, PA-22S-160, PA-22-135 - [TCDS A-691](https://openairdocs.org/tcds/A-691): Piper Aircraft Inc.; names 7 of 7 models: J3C-65 (Army L-4; L-4A; L-4B (Navy NE-1); L-4H; L-4J (Navy NE-2)), PA-11, J3C-40, PA-11S, J3C-65S, J3C-50, J3C-50S - [TCDS 1A4](https://openairdocs.org/tcds/1A4): Piper Aircraft Inc.; names 6 of 6 models: PA-20, PA-20S-135, PA-20-135, PA-20S-115, PA-20-115, PA-20S - [TCDS A-692](https://openairdocs.org/tcds/A-692): Piper Aircraft Inc.; names 6 of 6 models: J3F-60S, J3F-50S, J3F-65S, J3F-65 (Army L-4D), J3F-50, J3F-60 - [TCDS A-698](https://openairdocs.org/tcds/A-698): Piper Aircraft Inc.; names 4 of 4 models: J3L-65S, J3L, J3L-S, J3L-65 (Army L-4C) - [TCDS A-725](https://openairdocs.org/tcds/A-725): FS 2001 Corp.; names 4 of 6 models: J5B (Army L-4G), J5A-80, J5A (Army L-4F), J5C - [TCDS A-703](https://openairdocs.org/tcds/A-703): Piper Aircraft Inc.; names 3 of 3 models: J4A, J4A-S, J4 - [TCDS 1A1](https://openairdocs.org/tcds/1A1): Piper Aircraft Inc.; names 2 of 2 models: PA-16, PA-16S - [TCDS 1A15](https://openairdocs.org/tcds/1A15): Piper Aircraft Inc.; names 2 of 4 models: PA-24, PA-24-250 - [TCDS A-780](https://openairdocs.org/tcds/A-780): FS 2003 Corp.; names 2 of 2 models: PA-12S, PA-12 - [TCDS A-740](https://openairdocs.org/tcds/A-740): Piper Aircraft Inc.; names 1 of 1 models: J4E (Army L-4E) - [TCDS A-797](https://openairdocs.org/tcds/A-797): FS 2002 Corp.; names 1 of 1 models: PA-14 - [TCDS A-800](https://openairdocs.org/tcds/A-800): Piper Aircraft Inc.; names 1 of 1 models: PA-15 - [TCDS A-805](https://openairdocs.org/tcds/A-805): Piper Aircraft Inc.; names 1 of 1 models: PA-17 - [TCDS ATC 660](https://openairdocs.org/tcds/ATC%20660): Piper Aircraft Inc.; names 1 of 1 models: J-3 - [TCDS TC 695](https://openairdocs.org/tcds/TC%20695): Piper Aircraft Inc.; names 1 of 1 models: J3P - [TCDS TC 708](https://openairdocs.org/tcds/TC%20708): Piper Aircraft Inc.; names 1 of 1 models: J4B - [TCDS TC 721](https://openairdocs.org/tcds/TC%20721): Piper Aircraft Inc.; names 1 of 1 models: J4F ## 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: 11,870 (11,870 by airframe model, 0 by engine model) - Makers: Piper 11,785, Piper/Cub Crafters 46, Cub Crafters 16, Piper-Dahl 2, Cubs Unlimited/Piper 1, David B Piper 1, Kurt Lepping 1, Piper / Harris 1, Piper Whitaker 1, Piper-Carter 1 Models with the most aircraft: - [Piper PA-18-150](https://openairdocs.org/model/piper-pa-18-150): 2,065 aircraft (airframe model) - [Piper PA-12](https://openairdocs.org/model/piper-pa-12): 1,242 aircraft (airframe model) - [Piper PA-24-250](https://openairdocs.org/model/piper-pa-24-250): 1,222 aircraft (airframe model) - [Piper PA-22-150](https://openairdocs.org/model/piper-pa-22-150): 1,200 aircraft (airframe model) - [Piper PA-22-108](https://openairdocs.org/model/piper-pa-22-108): 587 aircraft (airframe model) - [Piper PA-18](https://openairdocs.org/model/piper-pa-18): 477 aircraft (airframe model) - [Piper PA-22-160](https://openairdocs.org/model/piper-pa-22-160): 456 aircraft (airframe model) - [Piper PA-11](https://openairdocs.org/model/piper-pa-11): 438 aircraft (airframe model) - [Piper PA-22-135](https://openairdocs.org/model/piper-pa-22-135): 409 aircraft (airframe model) - [Piper PA-18A 150](https://openairdocs.org/model/piper-pa-18a-150): 382 aircraft (airframe model) - [Piper PA-24](https://openairdocs.org/model/piper-pa-24): 345 aircraft (airframe model) - [Piper PA-22](https://openairdocs.org/model/piper-pa-22): 277 aircraft (airframe model) - [Piper PA-16](https://openairdocs.org/model/piper-pa-16): 276 aircraft (airframe model) - [Piper PA-20](https://openairdocs.org/model/piper-pa-20): 276 aircraft (airframe model) - [Piper J5A](https://openairdocs.org/model/piper-j5a): 268 aircraft (airframe model) - [Piper PA-18-135](https://openairdocs.org/model/piper-pa-18-135): 220 aircraft (airframe model) - [Piper J3L-65](https://openairdocs.org/model/piper-j3l-65): 179 aircraft (airframe model) - [Piper PA-15](https://openairdocs.org/model/piper-pa-15): 165 aircraft (airframe model) - [Piper PA-18A](https://openairdocs.org/model/piper-pa-18a): 152 aircraft (airframe model) - [Piper J3F-65](https://openairdocs.org/model/piper-j3f-65): 127 aircraft (airframe model) All 88 models: https://openairdocs.org/ad/68-05-01/models.md Every aircraft: https://openairdocs.org/ad/68-05-01/aircraft.md ## Related documents - [AC 43.13-1B CHG 1 Ed Update](https://openairdocs.org/ac/43.13-1): Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair. Cited as AC 43.13-1 in the AD's requirements ## NTSB investigations that cite this AD (3) 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 LAX07LA263](https://openairdocs.org/ntsb/LAX07LA263), Sep 2, 2007: Piper PA-22-150 (N13WA), Modesto, CA, destroyed. Probable cause: The failure of the airplane's exhaust muffler during takeoff that was due to an inadequate annual inspection. Contributing to the accident were the pilot's inadequate inspection to isolate the smoke… - [NTSB MIA00LA018](https://openairdocs.org/ntsb/MIA00LA018), Oct 29, 1999: Piper PA-22-150 (N2648P), Newberry, SC, substantial damage. Probable cause: a fire in the cockpit caused by the exhaust muffler, which resulted in a forced landing in a field, and subsequent impact with a berm. - [NTSB SEA96LA206](https://openairdocs.org/ntsb/SEA96LA206), Aug 30, 1996: Piper PA-22-108 (N4992Z), Ashland, OR, destroyed. Probable cause: inadequate inspection of the airplane by maintenance personnel,and a worn exhaust clamp, which resulted in a disconnected exhaust pipe, exhaust leak, burning and shorting of electrical wiring… --- 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.