Airworthiness Directives; Learjet Model 35, 35A, 36, and 36A Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Final rule.

SUMMARY:

This amendment adopts a new airworthiness directive (AD), applicable to all Learjet Model 35, 35A, 36, and 36A series airplanes, that requires revision of the Airplane Flight Manual (AFM) to add procedures for donning the flightcrew oxygen masks when the cabin altitude warning horn is activated. This amendment is intended to prevent incapacitation of the flightcrew due to lack of oxygen and consequent loss of control of the airplane due to absence of AFM procedures for donning the flightcrew oxygen masks when the cabin altitude warning horn is activated.

DATES:

Effective January 4, 2001.

ADDRESSES:

Information pertaining to this amendment may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas.

FOR FURTHER INFORMATION CONTACT:

Ben Sorensen, Flight Test Pilot, Flight Test and Program Management, ACE-117W, FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas 67209; telephone (316) 946-4165; fax (316) 946-4407.

SUPPLEMENTARY INFORMATION:

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to all Learjet Model 35, 35A, 36, and 36A series airplanes was published in the Federal Register on June 8, 2000 (65 FR 36391). That action proposed to require revision of the Airplane Flight Manual (AFM) to add procedures for donning the flightcrew oxygen masks when the cabin altitude warning horn is activated. That proposal was intended to prevent incapacitation of the flightcrew due to lack of oxygen and consequent loss of control of the airplane due to absence of AFM procedures for donning the flightcrew oxygen masks when the cabin altitude warning horn is activated.

Since the Issuance of the Proposal

The FAA has determined that the identified unsafe condition is adequately addressed by Step 1 (donning the oxygen mask following a cabin high altitude warning) of the AFM revision under paragraph (a) of the proposed AD. In line with that determination, it is no longer necessary to include Steps 2 through 12 of paragraph (a). The FAA has revised paragraph (a) of the final rule accordingly.

Comments on the Proposal

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Request To Withdraw the Proposal

One commenter states that it opposes the adoption of the proposal, as well as the FAA's continued efforts to use rulemaking to address “operational” concerns. The commenter contends that airworthiness directives should only address corrective actions that specifically identify product flaws that create an unsafe condition. In particular, the commenter maintains that the unsafe condition demands an “operational” as well as an educational concern. The commenter further states that its primary concern with the proposal is that, in the accidents and incidents reports where incapacitation of the flightcrew was due to hypoxia, the root design or mechanical flaw has not been identified. The commenter concludes that a pilot's failure to don an oxygen mask raises “operational” concerns that have nothing to do with the specific problems concerning the continued airworthiness of the product in question. From these comments, the FAA infers that the commenter requests that the proposed AD be withdrawn.

The FAA does not concur that the proposed AD should be withdrawn. The purpose of an AD is to correct an identified unsafe condition in products, regardless of where the unsafe condition is located or what it is caused by. The current AFM does not contain procedures to don oxygen masks when the cabin altitude aural warning is activated. The FAA considers that the lack of such procedures constitutes an unsafe condition and, as such, must be corrected. In essence, the requirement to revise the AFM to add procedures to don oxygen masks when the cabin altitude warning is activated serves to protect the flying public from the consequences of the unsafe condition. The AD also serves to protect the manufacturer from the liability that would be faced should the unsafe condition not be corrected.

Request To Revise the Emergency Procedures

One commenter requests that the proposed emergency descent procedures be revised to specify that the flightcrew (1) don the oxygen mask; (2) level off (stabilize) the aircraft; and (3) verify loss of cabin pressure. The commenter suggests that if loss of cabin pressure is verified, the flightcrew should continue with the remainder of the emergency procedures. The commenter states that the purpose of adding these steps would be to ensure that the procedures, as proposed, do not lead the flightcrew to a possible overreaction. The commenter concludes that the suggested additional steps would provide clear direction for the flightcrew when the cabin altitude warning horn activates.

The FAA does not concur with the request to add procedures specifying that, immediately after donning the oxygen masks, the flightcrew level off the aircraft and verify loss of cabin pressure. As explained previously, the FAA has determined that, other than donning the oxygen masks, it is unnecessary to add further requirements to the Emergency Procedures Section of the AFM. The current FAA-approved AFM appears to take a conservative approach to cabin high altitude emergency procedures and specifies that the flightcrew perform an emergency descent. Furthermore, the FAA has not identified any unsafe conditions associated with those specific AFM procedures. The FAA has, however, forwarded the commenter's suggestions to the manufacturer for its consideration.

Request To Revise the Title of the Emergency Procedures

One commenter, the manufacturer, requests that the title of the emergency procedures be revised to also address the condition where the flightcrew notices a high cabin altitude before the warning horn sounds. The commenter suggests that the following words be added to the title: “* * * or Cabin Altitude Exceeds 10,000 feet.”

The FAA finds that the suggested additional words will clarify and specify emergency procedures for a possible situation, and will encourage proactive flightcrew action. Therefore, the FAA concurs with the commenter's request, and has revised paragraph (a) of the AD accordingly.

Request To Add Certain Notes

One commenter, the manufacturer, also requests that two new notes be added to clarify the proposed requirements of paragraph (a) after Step 10 and Step 12.

The FAA does not concur. Since all steps except Step 1 of paragraph (a) of the proposal have been removed (as explained previously) from the proposed AD, it is unnecessary to provide further clarification of the other steps.

Request To Redesign the Oxygen System

Two commenters request that the proposal include a requirement that the oxygen bottle in the cockpit be redesigned to show oxygen bottle pressure and not system pressure. Additionally, one of those commenters requests that the oxygen bottle clearly indicate that the system is “on” during preflight.

The FAA does not concur that this AD should require redesign of the oxygen bottle system. The FAA finds that a properly conducted preflight of the oxygen masks will establish and verify the correct gauge that reads bottle pressure, and ensure that the oxygen bottle valve is properly positioned. Additionally, the required flow check will not work if the oxygen bottle is turned off since all oxygen would have been released from the system. The actions required in this AD are intended to sufficiently address the stated unsafe condition.

Since redesign of the oxygen bottle system was not specified in the proposal, to require such redesign in this AD would be to mandate requirements without benefit of opportunity for public comment. Since the FAA has received no reports of any unsafe conditions associated with the design of the indicating system or bottle pressure system, it is not considering further rulemaking at this time. However, the FAA has forwarded this suggestion to the manufacturer for its consideration.

Request To Add Additional Models to the Applicability

One commenter requests that the applicability be revised to include Learjet Model 23, early Model 24, and Model 25 series airplanes. The commenter states that the oxygen and pressurization systems on these airplanes are similar to the airplane models cited in the applicability of the proposed AD.

The FAA does not concur that additional airplane models should be added to the applicability of this AD. The FAA acknowledges that the oxygen and pressurization systems on those airplanes are similar to the Learjet Model 35 and 36 series airplanes. However, if those airplane models were added to the applicability of this AD, additional time for opportunity to comment would be required. The FAA finds that to delay this action would be inappropriate in light of the identified unsafe condition. If information is received that points to an unsafe condition on the Learjet Model 23, Model 24, or Model 25, the FAA will consider further rulemaking. The FAA will forward the commenter's suggestion to the airplane manufacturer.

Request To Identify Flight Conditions Where Emergency Descent Is Unnecessary

One commenter requests that the FAA identify all flight conditions in which an emergency descent is not required subsequent to donning oxygen masks, and clearly present the appropriate instructions in the final rule. The commenter notes that the proposed AD specifies that, regardless of the existing flight conditions, the flightcrew perform an emergency descent upon activation of the cabin altitude warning. The commenter points out that it is possible for the cabin altitude warning horn to activate during flight conditions that would not require an emergency descent and landing.

The FAA does not concur that identification of all flight conditions in which an emergency descent is not required is necessary. The FAA considers that the manufacturer has taken a prudent and conservative approach in establishing the current emergency descent procedures, which specify emergency descent is necessary regardless of flight conditions. However, for the reasons explained previously, other than donning the oxygen masks, the FAA has removed the requirement to complete additional emergency descent procedures from this final rule. Therefore, no change to the final rule is necessary in this regard.

Conclusion

After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

Cost Impact

There are approximately 739 Learjet Model 35, 35A, 36, and 36A series airplanes of the affected design in the worldwide fleet. The FAA estimates that 500 airplanes of U.S. registry will be affected by this AD, that it will take approximately 1 work hour per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $30,000, or $60 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

Regulatory Impact

The 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.

For the reasons discussed above, I certify that this action (1) is not a “significant regulatory action” under Executive Order 12866; (2) is not a “significant rule” under 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. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from 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

Adoption of the Amendment

Accordingly, 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:

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.

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

2000-24-19 Learjet: Amendment 39-12026. Docket 2000-NM-127-AD.

Applicability: Model 35, 35A, 36, and 36A series airplanes, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent incapacitation of the flightcrew and consequent loss of control of the airplane due to delays in donning oxygen masks in response to the activation of the cabin altitude warning horn, accomplish the following:

(a) Within 10 days after the effective date of this AD, revise the Emergency Procedures Section of the FAA-approved Airplane Flight Manual (AFM) by accomplishing the actions specified in paragraphs (a)(1) and (a)(2) of this AD:

(1) Revise the title for the existing “Emergency Descent” section to read:

“CABIN ALTITUDE WARNING HORN ACTIVATES OR CABIN ALTITUDE EXCEEDS 10,000 FEET (EMERGENCY DESCENT)”

(2) Insert the procedures specified below between the new, revised title specified in paragraph (a)(1) of this AD and the existing procedures for emergency descent specified in the AFM.

“Don Oxygen Masks and Select 100% oxygen.”

Alternative Methods of Compliance

(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, Wichita 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, Wichita ACO.

Note:

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

Special Flight Permit

(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.

Effective Date

(d) This amendment becomes effective on January 4, 2001.