This AD is prompted by a report of the failure of the engine fire shutoff switch in the engine fire control module, which resulted in the inability to stow the thrust reverser on a certain Boeing Model 767 series airplane. On this installation the thrust reverser is operated by engine pneumatic bleed air, which is regulated by a spring-loaded-closed pressure regulating and shutoff valve (PRSOV). The PRSOV requires electrical power to stay open against the spring force. Its power supply is routed through the engine fire shutoff switch. The electrical contacts for the thrust reverser inside the engine fire shutoff switch are normally in the closed position. When the engine fire shutoff switch is pulled, during a fire or test, the power supplied to the thrust reverser PRSOV is removed and the valve closes off the engine bleed air, leaving the thrust reverser in the last commanded position. Investigation of the reported incident revealed that certain flight deckhumidifiers distribute unfiltered air containing minerals from the potable water supply. The humidified air contaminates the auxiliary power unit (APU) and engine fire shutoff switches and may result in mineral build-up on switch contacts. The contamination within the fire shutoff switch gradually builds up, causing an increase in contact resistance. In the case of the thrust reverser, this contact resistance was high enough that the power supplied to the PRSOV was insufficient to hold the valve open. The PRSOV closed, leaving the thrust reverser in the deployed state. This same contamination can build up on the fire extinguishing switch contacts inside the APU and engine fire switches. Mineral build-up on the APU and engine fire shutoff switches, if not corrected, could lead to the switches failing to discharge fire suppressant to the affected fire zone and result in an uncontrolled engine or APU fire and consequent loss of the airplane. \n\nRelevant Service Information \n\n\tWe have reviewed Boeing Alert Service Bulletin 767-26A0127, dated July 17, 2003. The service bulletin describes the following procedures: \n\n\t1. Doing repetitive functional tests of the APU and engine fire shutoff switches; \n\n\t2. Doing repetitive replacements of the APU and engine fire shutoff switches with new or serviceable switches; and \n\t3. Deactivating the Lucas (also known as TRW Systemes Aeronautiques) flight deck humidifier, part numbers (P/N) M01AA0101, M01AB0101, M01AB0102, or M01AB0103, which eliminates the need for the repetitive functional tests and replacements. \n\tWe have determined that accomplishment of the actions specified in the service information will adequately address the unsafe condition. \n\nFAA's Determination and Requirements of This AD \n\n\tThe unsafe condition described previously is likely to exist or develop on other airplanes of the same type design that may be registered in the U.S. at some time in the future. Therefore, this AD is being issued to prevent mineral build-up on APU and engine fire shutoff switches, which could lead to the switches failing to discharge fire suppressant to the affected fire zone and result in an uncontrolled engine fire and consequent loss of the airplane. This AD requires repetitive functional tests and repetitive replacements of the APU and engine fire shutoff switches. This proposal also provides an optional terminating action for the repetitive functional tests and replacements. You must do these actions in accordance with the service information described previously, except as discussed under "Differences Between the AD and the Service Bulletin." \n\nDifferences Between the AD and the Service Bulletin \n\n\tOperators should note that the service bulletin specifies the initial compliance time as "after the airplane has 12 calendar months of service but within 18 calendar months since airplane delivery. * * *" This AD, however, specifies the initial compliance time as within 18 months since the date of issuance of the original Airworthiness Certificate or the original Export Certificate of Airworthiness. This decision is based on our determination that "since airplane delivery" may be interpreted differently by different operators. We find that this terminology is generally understood within the industry and records will always exist that establish these dates with certainty. This AD also omits reference to "after the airplane has 12 calendar months of service," since accomplishing the initial actions within 18 months of service provides an acceptable level of safety. Thus the compliance time specified in this AD includes any airplanes that may have been operating since delivery. \n\n\tOperators should also note that the service bulletin states, "Operators who perform the 90 calendar day inspection and the 18 calendar month switch servicing can avoid the required test interval shown in Figure 1, by deactivation of the Lucas (also known as TRW Systemes Aeronautiques) Flight Deck Humidifier." This AD, however, specifies that if an operator deactivates the flight deck humidifier, all APU and engine fire shutoff switches must be \nreplaced with new or serviceable switches before further flight. We have determined that if a flight deck humidifier is deactivated shortly before any required replacement or required functional test, it might be possible for any switch to have a latent type of failure due to the previous exposure to moisture and minerals from the humidifier. To address this unsafe condition, we have added a requirement to paragraph (j) of this AD to replace all switches after deactivating the flight deck humidifier. We have also added requirements to paragraph (k) of this AD to ensure an operator performs the repetitive functional tests and replacements of switches after reactivating the flight deck humidifier. \n\nCosts of Compliance \n\n\tNone of the airplanes affected by this action are on the U.S. Register. All airplanes affected by this AD are currently operated by non-U.S. operators under foreign registry; therefore, they are not directly affected by this AD action. However, we consider this AD necessary to ensure that the unsafe condition is addressed if any affected airplane is imported and placed on the U.S. Register in the future. \n\n\tIf an affected airplane is imported and placed on the U.S. Register in the future, the required functional test would take about 2 work hours per switch, at an average labor rate of $65 per work hour. We estimate there are 3 switches per airplane. No parts would be required. Based on these figures, the estimated cost of the AD would be $390 per airplane, per testing cycle. \n\n\tIf an affected airplane is imported and placed on the U.S. Register in the future, the required switch replacement would take about 2 work hours per switch, at an average labor rate of $65 per work hour. Required parts would cost about $1,000 per switch, if replaced with a serviceable switch. Based on these figures, the estimated cost of the AD would be $1,130 per switch, per replacement. \n\nFAA's Determination of the Effective Date \n\n\tNo airplane affected by this AD is currently on the U.S. Register. Therefore, providing notice and opportunity for public comment is unnecessary before this AD is issued, and this AD may be made effective in less than 30 days after it is published in the Federal Register. \n\nComments Invited \n\n\tAlthough this is a final rule that was not preceded by notice and an opportunity for public comment, we invite you to submit any written relevant data, views, or arguments regarding this AD. Send your comments to an address listed under ADDRESSES. Include "Docket No. FAA-2005-20010; Directorate Identifier 2003-NM-224-AD" at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD. We will consider all comments received by the closing date and may amend the AD in light of those comments. \n\n\tWewill 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 AD. Using the search function of our docket 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 the 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. \n\nAuthority for This Rulemaking \n\n\tThe FAA's authority to issue rules regarding aviation safety is found in Title 49 of the United States Code. 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. \n\n\tThis rulemaking is promulgatedunder 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 AD. \n\nRegulatory Findings \n\n\tWe have determined that this AD will not have federalism implications under Executive Order 13132. This AD will 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. \n\n\tFor the reasons discussed above, I certify that the regulation: \n\n\t1. Is not a "significant regulatory action" under Executive Order12866; \n\n\t2. Is not a "significant rule" under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\n\t3. 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. \n\n\tWe prepared a regulatory evaluation of the estimated costs to comply with this AD. See the ADDRESSES section for a location to examine the regulatory evaluation. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n2. The FAA amends Sec. 39.13 by adding the following new AD: