[Federal Register Volume 62, Number 62 (Tuesday, April 1, 1997)]
[Proposed Rules]
[Pages 15433-15435]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-8129]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-171-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-400, -400D, and -400F 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 747-400, -
400D, and -400F series airplanes. This proposal would require 
modification of the P212 and P213 panels of the cabin pressure control 
system. This proposal is prompted by a report of in-flight loss of 
cabin pressurization control due to a single failure of the auxiliary 
power unit (APU) battery. The actions specified by the proposed AD are 
intended to prevent loss of control of the cabin pressurization system, 
which could result in rapid depressurization of the airplane. Such 
rapid depressurization could result in deleterious physiological 
effects on the passengers and crew; and airplane diversions, which 
represent an increased risk to the airplane, passengers, and crew.

DATES: Comments must be received by May 9, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-171-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Clayton R. Morris, Jr., Aerospace 
Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (206) 227-2794; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed 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 above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 96-NM-171-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules 
Docket No. 96-NM-171-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA received a report indicating that power from the 28-volt 
direct current (DC) hot battery bus of the auxiliary power unit (APU) 
was lost during flight on a Model 747-400 series airplane. Loss of 
power from the hot battery bus resulted in loss of a discrete signal to 
both interface control units (ICU's). Loss of the discrete signal 
indicated that ``manual'' control mode was selected, but the cabin 
pressure control system was still in ``automatic'' control mode. The 
ICU's went into standby mode and transmitted this status to both cabin 
pressure controllers (CPC's). The CPC's then went into

[[Page 15434]]

standby mode and ceased trying to control the outflow valves.
    Loss of power from the hot battery bus also prevented the flight 
crew from driving the outflow valves in the ``manual'' control mode. 
When the ICU's went into standby mode, power to the outflow valve 
brakes was severed; this caused the brakes to engage. With the brakes 
engaged, the outflow valves were locked in the last commanded position. 
The flight crew reported receiving several engine indication and crew 
alerting system (EICAS) messages, and followed procedures to select the 
cabin pressurization control system to ``manual'' control mode.
    The airplane continued to cruise at an altitude of 35,000 feet 
without cabin pressurization problems. The cabin pressure differential 
at 35,000 feet was about 8.6 pounds per square inch differential 
(psid). (Cabin pressure differential is the difference between the 
airplane cabin pressure and the ambient pressure; 8.6 psid is 
considered to be normal at an altitude of 35,000 feet.)
    Later during the flight, the flight crew initiated a step climb to 
39,000 feet. The combination of both outflow valves being locked in the 
last commanded position and the decrease in ambient pressure [about 0.6 
pounds per square inch (psi)] due to the step climb caused the cabin 
pressure differential to increase to just over 9.1 psid. Both positive 
pressure relief valves opened due to the higher cabin pressure 
differential. With the air conditioning packs operating in ``Hi Flow'' 
mode and the positive pressure relief valves open, air conditioning 
pack number 2 automatically was commanded ``OFF.'' The flight crew also 
selected one of the two remaining air conditioning packs ``OFF.'' The 
loss of two-thirds of the cabin air inflow plus both outflow valves 
locking in the last commanded position caused the cabin pressure 
altitude to climb rapidly. At some point within two minutes after 
initiation of the step climb, the flight crew should have received a 
cabin pressure altitude warning at 10,000 feet and initiated an 
emergency descent. Analysis indicates that the cabin pressure altitude 
may have reached as high as 16,000 feet. The flight crew leveled off at 
14,000 feet and diverted the airplane.
    The flight crew landed the airplane about 50 minutes later with one 
air conditioning pack still operating, which caused the airplane to 
repressurize above the maximum pressure differential allowed to open 
the passenger doors. The flight crew turned off the last air 
conditioning pack about five minutes after landing (at a cabin pressure 
differential of about 0.7 psid). The airplane depressurized within one 
minute; the crew then was able to open the passenger doors.

Unsafe Conditions

    Because the flight crew could not control the cabin pressurization 
system during flight, rapid depressurization of the airplane occurred. 
Such rapid depressurization increases the potential for deleterious 
physiological effects on the passengers and crew. In addition, the 
inability to control cabin pressurization can result in airplane 
diversions, which represent an increased risk to the airplane, 
passengers, and crew due to the unplanned nature of the event and the 
potential for overweight landings.
    Additionally, when the cabin pressure differential exceeded the 
maximum pressure differential allowed to open the passenger doors after 
landing, the only means available to reduce the cabin pressure 
differential to a level low enough to allow the doors to be opened was 
through the airplane's inherent leakage. If an emergency condition 
existed upon landing (e.g., cabin fire, airplane fire, ditching, etc.) 
that required the passengers and crew to immediately exit the airplane, 
the crew would not have been able to open the passenger doors.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
747-21A2381, dated June 27, 1996, which describes procedures for 
modification of the P212 and P213 panels of the cabin pressure control 
system. Accomplishment of the modification entails the following:
    <bullet> For certain airplane groups: changing the wiring in the 
P212 and P213 panels; replacing the existing two-pole relays with new 
four-pole relays; and performing a test of both panels.
    <bullet> For one airplane group, accomplishment of the modification 
involves changing the wiring in the P212 panel; replacing the existing 
two-pole relays with new four-pole relays; replacing the existing P213 
panel with a new P213 panel; and performing a test of both panels.
    Accomplishment of the modification will provide power to the ICU 
and continuous auto control of cabin pressurization when the APU hot 
battery bus is lost.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require modification of the P212 and P213 panels of 
the cabin pressure control system. The actions would be required to be 
accomplished in accordance with the alert service bulletin described 
previously.

Cost Impact

    There are approximately 351 Boeing Model 747-400, -400D, and -400F 
series airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 43 airplanes of U.S. registry would be affected by this 
proposed AD, that it would take approximately 8 work hours per airplane 
to accomplish the proposed actions, and that the average labor rate is 
$60 per work hour. Required parts would cost approximately $389 per 
airplane. Based on these figures, the cost impact of the proposed AD on 
U.S. operators is estimated to be $37,367, or $869 per airplane.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the proposed requirements of 
this AD action, and that no operator would accomplish those actions in 
the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects 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, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (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) if promulgated, 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. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

[[Page 15435]]

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 96-NM-171-AD.
    Applicability: Model 747-400, -400D, and -400F series airplanes; 
as identified in Boeing Alert Service Bulletin 747-21A2381, dated 
June 27, 1996, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent loss of control of the cabin pressurization system, 
which could result in rapid depressurization of the airplane and 
consequent deleterious physiological effects on the passengers and 
crew; and airplane diversions, which represent an increased risk to 
the airplane, passengers, and crew; accomplish the following:
    (a) Within 180 days after the effective date of this AD, modify 
the P212 and P213 panels of the cabin pressure control system as 
specified in paragraph (a)(1) or (a)(2) of this AD, as applicable, 
in accordance with Boeing Alert Service Bulletin 747-21A2381, dated 
June 27, 1996.
    (1) For Groups 1 through 7 airplanes, as identified in the alert 
service bulletin: Change the wiring in the P212 and P213 panels; 
replace the existing two-pole relays with new four-pole relays; and 
perform a test of both panels.
    (2) For Group 8 airplanes, as identified in the alert service 
bulletin: Change the wiring in the P212 panel; replace the existing 
two-pole relays with new four-pole relays; replace the existing P213 
panel with a new P213 panel; and perform a test of both panels.
    (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, Transport Airplane Directorate. 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.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (c) 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.

    Issued in Renton, Washington, on March 25, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-8129 Filed 3-31-97; 8:45 am]
BILLING CODE 4910-13-U