Priority Letter AD 98-02-05 on the Cessna 172R

U.S. Department of Transportation Federal Aviation Administration
PRIORITY LETTER

AIRWORTHINESS DIRECTIVE REGULATORY SUPPORT DIVISION
P.O. BOX 26460
OKLAHOMA CITY, OKLAHOMA73125-0460

DATE: January 9, 1998 98-02-05

This priority letter Airworthiness Directive (AD) is prompted by reports of thepotential for carbon monoxide gas to leak into the cabin heating system and the cabin ofcertain Cessna Model 172R airplanes. This condition, if not corrected, could result inpassenger and pilot injury with consequent loss of control of the airplane.

Cessna Aircraft Company has reported that a quality control problem exists withAeroquip engine exhaust mufflers installed on certain Cessna Model 172R airplanes. Cessnarecently notified the FAA that the Aeroquip muffler, part number (P/N) 00624-NH4000011-1071379 0554011-2, is installed in approximately 250 Cessna Model 172R airplanes. Cessna hasalready determined through pressure testing that approximately 5 out of the 25 testedmufflers manufactured by Aeroquip are leaking. These inadequate or failed weldments willpermit exhaust gas (including carbon monoxide) leakage from the muffler, and consequentlyinto the airplane's cabin and cock-pit area.

After examining the circumstances and reviewing all information related to thesituation described above, the FAA has determined that AD action should be taken on CessnaModel 172R airplanes to prevent carbon monox-ide gas from entering the airplane's cabinheating system and cabin, which, if not corrected, could result in passenger and pilotinjury with consequent loss of control of the airplane. Since an unsafe condition has beenidentified (carbon monoxide leakage into the cabin area) that is likely to exist ordevelop on other Cessna Model 172R airplanes of this same type design, this AD requires,prior to further flight (1) de-activating the cabin heating system, and (2) fabricatingand installing a placard within the pilot's clear view, using 1/8-inch letters with thefollowing words: "CABIN HEATER INOPERATIVE."

This AD also requires, within the next 50 hours time-in-service (TIS), replacing theAeroquip engine exhaust muffler (P/N 00624-NH4000011-10 71379 0554011-2). If replacementparts are not available, the airplane may continue operation with the heating systemdisabled for a period not to exceed 6 calendar months after the effective date of this AD.

This rule is issued under 49 U.S.C. Section 44701 (formerly section 601 of the FederalAviation Act of 1958), pursuant to the authority delegated to me by the Administrator, andis effective immediately upon receipt of this priority letter.

98-02-05 CESSNA AIRCRAFT COMPANY: Priority Letter issued on January 9, 1998. Docket No.98-CE-06-AD.

Applicability: Model 172R airplanes (Serial Numbers 17280001 through 17280305),certified in any category, that are equipped with an Aeroquip engine exhaust muffler (P/N00624-NH4000011-10 71379 0554011-2).

NOTE 1: The letters "PT" or "PTT" stamped in the right-handexternal ring that supports the muffler cabin heater shroud indicate that Cessna has builtor re-built the part. Parts marked in this manner are not Aeroquip parts.

NOTE 2: This AD applies to each airplane identified in the precedingapplicability provision, regardless of whether it has been modified, altered, or repairedin the area subject to the requirements of this AD. For airplanes that have been modified,altered, or repaired so that the performance of the requirements of this AD is affected,the owner/operator must request approval for an alternative method of compliance inaccordance with paragraph (h) of this AD. The request should include an assessment of theeffect of the modification, alteration, or repair on the unsafe condition addressed bythis AD; and, if the unsafe condition has not been eliminated, the request should includespecific proposed actions to address it.

Compliance: Required as indicated in the body of this priority letter AD, unlessalready accomplished. To prevent carbon monoxide gas from entering the airplanescabin heating system and cabin, which, if not corrected, could result in passenger andpilot injury with consequent loss of control of the airplane, accomplish the following:

(a) Prior to further flight after receipt of this priority letter, AD, de-activate thecabin heating system by ensuring that the valve mechanism is functional, and that thecabin heat valve lever is safety wired in the down "off" position.

(b) Prior to further flight after receipt of this priority letter AD, fabricate andinstall a placard near the cabin heat control knob, within the pilot's clear view, usingat least 1/8-inch letters with the following words: "CABIN HEATER INOPERATIVE"

(c) Within the next 50 hours time-in-service (TIS) after receipt of this priorityletter AD, replace the engine exhaust muffler with a muffler having one of the followingpart numbers (P/N) in accordance with the appropriate Cessna maintenance manual:00624-NH4000011-10 71379 0554011-2-PTT, or 0554011-2, or 0554011-6, or an FAA-approvedequivalent part number.

NOTE 3: P/N 0554011-2 will have "PT" stamped on the right-handexternal ring that supports the muffler; and P/N 0554011-6 may have "PT" stampedon the right-hand external ring.

(d) If parts are not available for the replacement required in paragraph (c) of thisAD, the airplane may continue to be operated for a period not to exceed 6 calendar monthsfrom the date of receipt of this priority letter AD, provided the cabin heating systemremains de-activated.

(e) The cabin heating system may be re-activated and the placard required in paragraph(b) of this AD may be removed, once the muffler is replaced in accordance with thispriority letter AD.

(f) After receipt of this priority letter AD, no person may install any Aeroquip engineexhaust muffler, P/N 00624-NH4000011-10 71379 0554011-2, on any Cessna Model 172Rairplane.

(g) Special flight permits may be issued in accordance with sections 21.197 and 21.199of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane toa location where the requirements of this AD can be accomplished, provided the airplanecabin heater system is not used during that flight.

(h) An alternative method of compliance or adjustment of the compliance times thatprovides an equiva-lent level of safety may be approved by the Manager, Wichita AircraftCertification Office, 1801 Airport Road, Rm. 100, Mid-Continent Airport, Wichita, Kansas67209. The request shall be forwarded through an appropriate FAA Maintenance Inspector,who may concur or comment and then send it to the Manager, Wichita Aircraft CertificationOffice.

NOTE 4: Information concerning the existence of approved alternative methods ofcompliance with this AD, if any, may be obtained from the Wichita Aircraft CertificationOffice.

(i) Copies of this priority letter AD may be examined at the FAA, Central Region,Office of the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri64106.

(j) Priority Letter AD 98-02-05, issued January 9, 1998, becomes effective immediatelyupon receipt.

FOR FURTHER INFORMATION CONTACT:

Mr. Paul Pendleton, Aerospace Engineer Wichita Aircraft Certification Office, 1801Airport Road, Rm. 100, Mid-Continent Airport, Wichita, Kansas 67209, telephone (316)946-4143; facsimile (316) 946-4407.