E8-9193. Airworthiness Directives; Boeing Model 737 Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737 airplanes. This proposed AD would require repetitive inspections, lubrications, and repetitive repairs/overhauls of the ball nut and ballscrew and attachment (Gimbal) fittings for the trim actuator of the horizontal stabilizer; various installation(s); and corrective actions if necessary; as applicable. This proposed AD results from a report of extensive corrosion of a ballscrew used in the drive mechanism of the horizontal stabilizer trim actuator (HSTA). We are proposing this AD to prevent an undetected failure of the primary load path for the ballscrew in the drive mechanism of the HSTA and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.

DATES:

We must receive comments on this proposed AD by June 12, 2008.

ADDRESSES:

You may send comments by any of the following methods:

• Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
• Fax: [phone].
• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this AD, contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov;​; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (telephone [phone]) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Kelly McGuckin, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send any written relevant data, views, or arguments about this proposed AD. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2008-0415; Directorate Identifier 2007-NM-256-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov,, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.

Discussion

On January 31, 2000, there was an accident involving a McDonnell Douglas Model DC-9-83 (MD-83) airplane. The National Transportation Safety Board (NTSB) determined that the probable cause of the accident was a loss of airplane pitch control resulting from the in-flight failure of the acme nut threads of the jackscrew assembly of the horizontal stabilizer trim system. The NTSB concluded that the thread failure was caused by excessive wear, resulting from insufficient lubrication of the jackscrew assembly. The drive mechanism of the horizontal stabilizer on Model MD-83 airplanes has a jackscrew assembly with an acme screw. The drive mechanism of the horizontal stabilizer on Boeing Model 737 airplanes has a horizontal stabilizer trim actuator (HSTA) with a ballscrew. Acme screws and ballscrews have some differences in design, but perform similar functions and have the same airplane-level effect following failure.

In response to this accident, Boeing initiated a design review and safety analysis of the primary and secondary load paths of the ballscrew assembly used on the HSTA of their airplanes. During this review, one operator of a Model 757 airplane reported extensive corrosion of a ballscrew assembly of the HSTA. Investigation revealed extensive corrosion of the primary load path ball bearings in the ballscrew assembly. This condition, if not corrected, could result in an undetected failure of the primary load path for the ballscrew in the drive mechanism of the HSTA and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.

The ballscrew assembly on Model 757 airplanes is similar to those on the affected Model 737 airplanes. Therefore, all of these models may be subject to the same unsafe condition.

Other Relevant Rulemaking

We are considering additional rulemaking to address the identified unsafe condition on Model 757 airplanes.

Relevant Service Information

We have reviewed the following Boeing Service Bulletins:

Table—Primary Service Bulletins

Boeing Alert Service Bulletin—	Describes the following procedures for the trim actuator of the horizontal stabilizer (depending on the airplane configuration)—	And recommends that those actions be done—
737-27A1277, Revision 1, dated July 25, 2007 (for Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes)	Repetitive detailed and general visual inspections to detect discrepancies (e.g., metal particles or corrosion in grease, damage, cracks, corrosion, worn areas, grease leakage, and loose ball bearings) of the ball nut and ballscrew	Within 6,400 flight hours or 18 months from the last detailed inspection, whichever occurs first, and thereafter at intervals not to exceed 6,400 flight hours or 2 years, whichever occurs first.
	Repetitive lubrications of the ball nut and ballscrew	Within 1,600 flight hours or 1 year from the last lubrication, whichever occurs first, and thereafter at intervals not to exceed 1,600 flight hours or 1 year, whichever occurs first.
	Repetitive repair/overhaul	Before the accumulation of 25,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 25,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer, whichever occurs first, and thereafter at intervals not to exceed 25,000 flight hours.
	Installation of tube retainers on the ball nut	Before the accumulation of 25,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 25,000 flight hours since the latest overhaul of the trim actuator of the horizontal stabilizer, whichever occurs later.
	Applicable corrective actions. The corrective actions include repairing/replacing discrepant parts	Before further flight.
737-27A1278, dated May 24, 2007 (for Model 737-100, -200, -200C, -300, -400, and -500 series airplanes)	Repetitive detailed and general visual inspections to detect discrepancies (e.g., metal particles or corrosion in grease, damage, cracks, corrosion, worn areas, grease leakage, and loose ball bearings) of the ball nut and ballscrew and attachment (Gimbal) fittings	Within 2,000 or 4,000 flight hours or 12 or 18 months from the last detailed inspection, whichever occurs first, and thereafter at intervals not to exceed 2,000 or 4,000 flight hours or 1 or 2 years, whichever occurs first (depending on the airplane configuration).
	Repetitive lubrications of the ball nut and ballscrew and attachment (Gimbal) fittings	Within 500 or 2,000 flight hours or 2 months or 1 year from the last lubrication, whichever occurs first, and thereafter at intervals not to exceed 500 or 2,000 flight hours or 2 months or 1 year, whichever occurs first (depending on the airplane configuration).
	Repetitive repair/overhaul	Before the accumulation of 20,000 flight hours or 24,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 20,000 flight hours or 24,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer, whichever occurs first (depending on the airplane configuration); and thereafter at intervals not to exceed 20,000 or 25,000 flight cycles (depending on the airplane configuration).
	Installation of tube retainers on the ball nut	Before the accumulation of 24,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 24,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer, whichever occurs first.
	Installation of a grease fitting	Before the accumulation of 20,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 20,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer, whichever occurs first.
	Installation of new ball deflectors and guide clamps for the ball return	Before the accumulation of 24,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 24,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer, whichever occurs first.
	Installation of new return tube clamps	Before the accumulation of 20,000 flight hours since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, or within 20,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer, whichever occurs first.
	Applicable corrective actions. The corrective actions include repairing/replacing discrepant parts	Before further flight.

Table.—Secondary Service Bulletins

Boeing Alert Service Bulletin—	Refers to—
737-27A1277, Revision 1, dated July 25, 2007 (for Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes)	UMBRA CUSCINETTI Service Bulletin 07322-27-01, dated December 21, 2004, as an additional source of service information for installing tube retainers on the ball nut.
737-27A1278, dated May 24, 2007 (for Model 737-100, -200, -200C, -300, -400, and -500 series airplanes)	UMBRA CUSCINETTI Service Bulletin 07322-27-01, dated December 21, 2004, as an additional source of service information for installing tube retainers on the ball nut.
	Boeing 737 Service Bulletin 27-1046, Revision 1, dated April 5, 1974, as an additional source of service information for installing a grease fitting.
	Linear Motion Service Bulletin 7901708, Revision A, dated July 26, 2005, as an additional source of service information for installing new ball deflectors and guide clamps for the ball return.
	SKYTRONICS Service Bulletin 93004, dated September 1, 2005, as an additional source of service information for installing new return tube clamps.

FAA's Determination and Requirements of This Proposed AD

We are proposing this AD because we evaluated all relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the(se) same type design(s). This proposed AD would require accomplishing the actions specified in the primary service bulletins described previously.

Clarification of Applicability of This AD

Boeing has informed us that Model 737-900ER series airplanes were not specifically identified by model name in the Effectivity section of Boeing Alert Service Bulletin 737-27A1277. However, those airplanes are identified by variable numbers in the Effectivity section. Therefore, this AD refers to Model 737-900ER series airplanes where appropriate.

Costs of Compliance

We estimate that this proposed AD would affect 1,602 Model 737 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

Estimated Costs

Action 1	Work hours 1	Average labor rate per hour	Parts	Cost per product 1	Number of U.S.-registered airplanes	Fleet cost 1
Detailed inspections	2 or 4	$80	None	$160 or $320, per inspection cycle	1,602	Between $256,320, and $512,640 per inspection cycle.
Lubrications	1 or 3	80	None	$80 or $240, per lubrication cycle	1,602	Between $128,160, and $384,480 per lubrication cycle.
Repairs/overhauls	40	80	None	$3,200 per repair/overhaul	1,602	$5,126,400 per repair/overhaul cycle.
Installations	Between 1 and 3	80	$2,200	Between $2,280 and $2,440	1,320	Between $3,009,600 and $3,220,800.
1 Depending on airplane configuration.

The number of work hours, as indicated above, is presented as if the accomplishment of the actions in this proposed AD is to be conducted as new “stand alone” actions. However, in actual practice, the lubrications, detailed inspections, and overhauls are currently being done as part of normal airplane maintenance. The repair can be done coincidentally or in combination with the normally scheduled HSTA and ballscrew overhaul. Therefore, the actual number of necessary additional work hours will be minimal in many instances. Additionally, any costs associated with special airplane scheduling will be minimal.

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 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 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. 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.

You can find our regulatory evaluation and the estimated costs of compliance in the AD Docket.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 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.

§ 39.13

[Amended]

2. The FAA amends § 39.13 by adding the following new AD:

Boeing: Docket No. FAA-2008-0415; Directorate Identifier 2007-NM-256-AD.

Comments Due Date

(a) We must receive comments by June 12, 2008.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing airplanes identified in Table 1 of this AD, certificated in any category.

Table 1.—Applicability

Boeing model—	As identified in Boeing Alert Service Bulletin—
(1) 737-100, -200, -200C, -300, -400, and -500 series airplanes	737-27A1278, dated May 24, 2007.
(2) 737-600, -700, -700C, -800, -900, and -900ER series airplanes	737-27A1277, Revision 1, dated July 25, 2007.

Unsafe Condition

(d) This AD results from a report of extensive corrosion of a ballscrew in the drive mechanism of the horizontal stabilizer trim actuator (HSTA). We are issuing this AD to prevent an undetected failure of the primary load path for the ballscrew in the drive mechanism of the HSTA and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.

Compliance

(e) Comply with this AD within the compliance times specified, unless already done.

Service Bulletins

(f) The term “service bulletin,” as used in this AD, means the applicable service bulletins specified in Table 2 of this AD.

Table 2.—Service Bulletins

Boeing Alert Service Bulletin—	For model—
(1) 737-27A1278, dated May 24, 2007	737-100, -200, -200C, -300, -400, and -500 series airplanes.
(2) 737-27A1277, Revision 1, dated July 25, 2007	737-600, -700, -700C, -800, -900, and -900ER series airplanes.

Note 1:

The service bulletins refer to UMBRA CUSCINETTI Service Bulletin 07322-27-01, dated December 21, 2004; Linear Motion Service Bulletin 7901708, Revision A, dated July 26, 2005; Boeing 737 Service Bulletin 27-1046, Revision 1, dated April 5, 1974; and/or SKYTRONICS Service Bulletin 93004, dated September 1, 2005, as applicable, as additional sources of service information for accomplishing the specified actions.

Inspections, Lubrications, Repairs/Overhauls, and Applicable Corrective Actions

(g) At the applicable compliance time and repeat intervals listed in Tables 1 and 2 of paragraph 1.E., “Compliance,” of the service bulletin, do the inspections, lubrications, repairs/overhauls, installation(s), and applicable corrective actions by accomplishing all the applicable actions specified in the Accomplishment Instructions of the service bulletin; except as provided by paragraphs (g)(1) through (g)(3) of this AD.

(1) Where paragraph 1.E., “Compliance,” of the service bulletin specifies an initial compliance time for accomplishing the initial inspection, lubrication, or repair/overhaul, this AD requires doing the applicable initial action(s) at the later of the times specified in paragraphs (g)(1)(i) and (g)(1)(ii) of this AD.

(i) At the applicable compliance time specified in paragraph 1.E., “Compliance,” of the service bulletin.

(ii) Within the applicable compliance time specified in paragraph (g)(1)(ii)(A), (g)(1)(ii)(B), or (g)(1)(ii)(C) of this AD.

(A) For the initial detailed inspection and lubrication: Within 6 months after the effective date of this AD.

(B) For the initial repair/overhaul: Within 12 months after the effective date of this AD.

(C) For the installation(s): Within 12 months after the effective date of this AD.

(2) Where Table 2 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, specifies a compliance time of “* * * within 25,000 Flight Hours since the latest horizontal stabilizer trim actuator (HSTA) Overhaul from the date of Revision 1 of this Service Bulletin * * *,” this AD requires compliance “* * * within 25,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer.”

(3) Where Work Package 4, paragraphs 1.a., 2.a., and 3.a., of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007, specifies to identify the HSTA name plate “* * * AS GIVEN IN SB 737-27A1278, WORK PACKAGE 3,” this AD requires that identification “ * * * AS GIVEN IN SB 737-27A1278, WORK PACKAGE 4.”

(4) Where Note (b) of Figures 7 through 9 of Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007, specifies to do a “* * * Backlash Inspection as given in AMM 27-41-81/606,” this AD requires an “* * * End Play Test as given in OHM 27-45-11 page 701.”

(h) Actions done before the effective date of this AD in accordance with Boeing Alert Service Bulletin 737-27A1277, dated July 21, 2005, are acceptable for compliance with the corresponding requirements of this AD.

Alternative Methods of Compliance (AMOCs)

(i)(1) The Manager, Seattle Aircraft Certification Office, FAA, ATTN: Kelly McGuckin, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone]; has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19.

(2) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO.

Issued in Renton, Washington, on April 17, 2008.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.