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

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

AIRWORTHINESS DIRECTIVE REGULATORY SUPPORT DIVISION
P.O. BOX 26460
OKLAHOMA CITY, OKLAHOMA 73125-0460

DATE: January 9, 1998 98-02-05

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

Cessna Aircraft Company has reported that a quality control problem exists with Aeroquip engine exhaust mufflers installed on certain Cessna Model 172R airplanes. Cessna recently notified the FAA that the Aeroquip muffler, part number (P/N) 00624-NH4000011-10 71379 0554011-2, is installed in approximately 250 Cessna Model 172R airplanes. Cessna has already determined through pressure testing that approximately 5 out of the 25 tested mufflers manufactured by Aeroquip are leaking. These inadequate or failed weldments will permit exhaust gas (including carbon monoxide) leakage from the muffler, and consequently into the airplane's cabin and cock-pit area.

After examining the circumstances and reviewing all information related to the situation described above, the FAA has determined that AD action should be taken on Cessna Model 172R airplanes to prevent carbon monox-ide gas from entering the airplane's cabin heating system and cabin, which, if not corrected, could result in passenger and pilot injury with consequent loss of control of the airplane. Since an unsafe condition has been identified (carbon monoxide leakage into the cabin area) that is likely to exist or develop 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) fabricating and installing a placard within the pilot's clear view, using 1/8-inch letters with the following words: "CABIN HEATER INOPERATIVE."

This AD also requires, within the next 50 hours time-in-service (TIS), replacing the Aeroquip engine exhaust muffler (P/N 00624-NH4000011-10 71379 0554011-2). If replacement parts are not available, the airplane may continue operation with the heating system disabled 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 Federal Aviation Act of 1958), pursuant to the authority delegated to me by the Administrator, and is 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/N 00624-NH4000011-10 71379 0554011-2).

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

NOTE 2: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in 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 in accordance with paragraph (h) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated in the body of this priority letter AD, unless already accomplished. To prevent carbon monoxide gas from entering the airplanes cabin heating system and cabin, which, if not corrected, could result in passenger and pilot 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 the cabin heating system by ensuring that the valve mechanism is functional, and that the cabin heat valve lever is safety wired in the down "off" position.

(b) Prior to further flight after receipt of this priority letter AD, fabricate and install a placard near the cabin heat control knob, within the pilot's clear view, using at 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 priority letter AD, replace the engine exhaust muffler with a muffler having one of the following part 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-approved equivalent part number.

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

(d) If parts are not available for the replacement required in paragraph (c) of this AD, the airplane may continue to be operated for a period not to exceed 6 calendar months from the date of receipt of this priority letter AD, provided the cabin heating system remains 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 this priority letter AD.

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

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

(h) An alternative method of compliance or adjustment of the compliance times that provides an equiva-lent level of safety may be approved by the Manager, Wichita Aircraft Certification Office, 1801 Airport Road, Rm. 100, Mid-Continent Airport, Wichita, Kansas 67209. 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 Certification Office.

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

(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, Missouri 64106.

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

FOR FURTHER INFORMATION CONTACT:

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