SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to submit any relevant written data, views, or arguments regarding this proposed AD. Include the docket number “FAA-2005-22558; Directorate Identifier 2005-NM-107-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://dms.dot.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of that web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov.

Examining the Docket

You may examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647-5227) is located on the plaza level of the Nassif Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them.

Discussion

We have received a report indicating that the auxiliary power unit (APU) fire extinguishing system was mis-wired on some Cessna Model 750 airplanes. Although the main engine fire extinguishing system on all Cessna Model 750 airplanes is wired correctly, further investigation revealed that the fire extinguishing systems on the main engines of Cessna Model 500, 550, S550, 560 airplanes, and on the main engines and APUs of Cessna Model 560XL airplanes may not be wired correctly. Therefore, all of these models may be subject to the same or similar unsafe condition found on the Cessna Model 750 APU installation. The engine and APU fire extinguishing bottles on these airplane models have positive and negative terminal studs that are the same size, so it is possible to cross-connect the wiring of the positive and negative leads. If the wiring is cross-connected and the fire extinguishing bottles are activated, the circuit breaker may trip due to the direct ground on the positive lead, and no fire extinguishing agent would be expelled. In addition, with the exception of the Model 750 APU installation, the tripped circuit breaker removes power from the fuel and hydraulic firewall shutoff valves, which are powered closed from a normally open state, and from the associated cockpit indications. As a result, flammable fluids could continue to be supplied to the area during a fire. It should be noted that the APU ( printed page 57214) installation on the Cessna Model 750 airplanes has a solenoid valve that is powered open from the normally closed state and would close to shut off fuel with the disruption of power. The circuit breaker that provides power to the extinguishing bottle differs from the circuit breaker that controls the shutoff valve that is powered on. Finally, the flightcrew would know that the fire had not been extinguished because the engine fire annunciator would stay illuminated, and the annunciators for the firewall shutoff valve may not illuminate if the valve does not close. Thus, the flightcrew would not know why the fire had not been extinguished. These conditions, if not corrected, could result in an unextinguished fire in the nacelle or APU.

Relevant Service Information

We have reviewed the Cessna service bulletins in the table below.

The service bulletins describe procedures for installing identification sleeves on the wires for the positive and negative terminal studs of the engine and/or APU fire extinguishing bottles; re-connecting the wires to the correct studs; testing the connection; and, for all but the Cessna Model 750 airplanes, re-connecting the wires if necessary until the connection tests correctly. For Cessna Model 500, 550, S550, and 560 airplanes, these actions are done for the engine fire extinguishing bottles only. For Cessna Model 750 airplanes, these actions are done for the APU fire extinguishing bottle only. For Cessna Model 560XL airplanes, this action is done for both the engine and the APU fire extinguishing bottles. The service bulletins also specify that operators should send a maintenance transaction report to the manufacturer. Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other airplanes of this same type design. For this reason, we are proposing this AD, which would require accomplishing the actions specified in the service information described previously, except as discussed under “Differences Between the Proposed AD and the Service Bulletins.”

Differences Between the Proposed AD and the Service Bulletins

Operators should note that, although the Accomplishment Instructions of the referenced service bulletins describe procedures for submitting a maintenance transaction report to the manufacturer, this proposed AD would not require that action. We do not need this information from operators.

Clarification of Service Bulletin 750-26-05

Although Cessna Service Bulletin 750-26-05 does not specify procedures for re-connecting the wires if necessary until the connection tests correctly, that action is implied in the service bulletin and would be required in this proposed AD.

Costs of Compliance

There are about 2,801 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in subtitle VII, part A, subpart III, section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Regulatory Findings

We have determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify that the proposed regulation: ( printed page 57215)

1. Is not a “significant regulatory action” under Executive Order 12866;

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

3. Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation.

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows: