AD 2002-14-20

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-600, -700, -800, and -900 series airplanes. This action requires measuring the electrical voltage at the circuit breaker for a certain pitot heater to determine if the pitot heater is connected to the correct power supply bus, and performing corrective action, if necessary. This action is necessary to prevent ice from blocking the pitot tube that provides airspeed data to the captain. Such ice blockage could lead to the flightcrew receiving incorrect airspeed data, which could result in loss of control of the airplane if the flightcrew fails to recognize that the data are incorrect. This action is intended to address the identified unsafe condition.

Final rule; request for comments.

2002-14-20 Boeing: Amendment 39-12820. Docket 2002-NM-127-AD. \n\n\tApplicability: Model 737-600, -700, -800, and -900 series airplanes; as listed in Boeing Alert Service Bulletin 737-24A1150, dated April 11, 2002; certificated in any category. \n\n\tNote 1: 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 (b) 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. \n\n\tCompliance:Required as indicated, unless accomplished previously. \n\n\tTo prevent ice from blocking the pitot tube that provides airspeed data to the flightcrew, which could lead to the flightcrew receiving incorrect airspeed data, and result in loss of control of the airplane if the flightcrew fails to recognize that the data are incorrect, accomplish the following: \n\nMeasurement of Voltage and Corrective Actions \n\n\t(a) Within 60 days after the effective date of this AD, measure the electrical voltage at the circuit breaker for the captain's pitot heater to determine if the pitot heater is connected to the correct power supply bus, per Boeing Alert Service Bulletin 737-24A1150, dated April 11, 2002. \n\n\t\t(1) If the measurement is 100 to 122 volts alternating current (AC): No further action is required by this AD. \n\n\t\t(2) If the measurement is not 100 to 122 volts AC: Before further flight, perform all actions associated with connecting the subject circuit breaker wire to the 115-volt ACstandby power supply bus (including performing a test to ensure that the pitot heater system operates correctly, repeating the measurement of the electrical voltage at the circuit breaker for the captain's pitot heater, and troubleshooting and correcting the wire connections until the test and measurement are successful), per the service bulletin. \n\nAlternative Methods of Compliance \n\n\t(b) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n\n\tNote 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\nSpecial Flight Permits \n\n\t(c) Special flight permits may be issued inaccordance 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. \n\nIncorporation by Reference \n\n\t(d) The actions shall be done in accordance with Boeing Alert Service Bulletin 737-24A1150, dated April 11, 2002. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\nEffective Date \n\n\t(e) This amendment becomes effective on July 31, 2002.

The FAA has received reports indicating that, on certain Boeing Model 737-600, -700, -800, and -900 series airplanes, the captain's indicated airspeed sensor and the captain's display unit may give inconsistent airspeed data to the flightcrew. Investigation of two incidents has revealed that, during production, the circuit breaker wire for the captain's pitot heater was connected to the 28-volt alternating current (AC) power supply bus, instead of the 115-volt AC standby power supply bus. The 28-volt power supply bus does not supply sufficient electrical power to heat the captain's pitot probe and keep it free of ice. This condition, if not corrected, could cause ice blockage of the captain's pitot probe, leading to the flightcrew receiving incorrect airspeed data, which could result in loss of control of the airplane if the flightcrew fails to recognize that the data are incorrect. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 737-24A1150, dated April 11, 2002, which describes procedures for measuring the electrical voltage at the circuit breaker for the captain's pitot heater to determine if the pitot heater is connected to the correct power supply bus, and performing corrective action, if necessary. The corrective action involves connecting the subject circuit breaker wire to the 115-volt AC standby power supply bus, performing a test to ensure that the pitot heater system operates correctly, and repeating the measurement of the electrical voltage at the circuit breaker for the captain's pitot heater. If the test fails or the electrical voltage is still incorrect, the service bulletin specifies to troubleshoot the problem and repeat the corrective actions. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. \n\nExplanation of the Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent ice from blocking the pitot tube that provides airspeed data to the captain, which could lead to the flightcrew receiving incorrect airspeed data and result in loss of control of the airplane if the flightcrew fails to recognize that the data are incorrect. This AD requires accomplishment of the actions specified in the service bulletin described previously, except as discussed below. \n\nDifference Between Service Information and This AD \n\n\tWhile the service bulletin specifies that no further action is necessary if the voltage measurement of the circuit breaker for the captain's pitot heater is 115 volts AC, paragraph (a)(1) of this AD states that, if the measurement is between 100 and 122 volts AC, no further action is required by this AD. The range of 100 to 122 volts AC specified in this AD accounts for normal variances that may be encountered duringthe voltage measurement. \n\nDetermination of Rule's Effective Date \n\n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tSubmit comments using the following format: \n\nOrganize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues. \n\nFor each issue, state what specific change to the AD is being requested. \n\nInclude justification (e.g., reasons or data) for each request. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2002-NM-127-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. \n\n\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. \n\n\tA copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ADDRESSES. \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\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39-AIRWORTHINESS DIRECTIVES \n\n\t1. 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\n\t2. Section39.13 is amended by adding the following new airworthiness directive: