98-15-25 EUROCOPTER DEUTSCHLAND [R3/15H]

	This Priority Letter Airworthiness Directive (AD) is prompted by reports of loose tail rotor drive shaft bearings (bearings) and attachment bolts.  Prompted by similar reports, the FAA previously issued AD 98-09-11 on June 18, 1998 (63 FR 34796, June 26, 1998), which required, before further flight, a review of aircraft records to determine if a tail rotor drive shaft vibration survey and installation of a Fenestron Shaft Retrofit Kit have been accomplished; before further flight, and thereafter at intervals not to exceed 15 hours time-in-service (TIS), inspecting the bearing attaching lock plates for bent-open tabs, and broken or missing slippage marks; and visually inspecting each bearing support for cracks.
	Since the issuance of AD 98-09-11, the manufacturer has determined that cracks can form in additional areas outside the bend radius of the bearing support, and that the cracks can form and propagate to failure within the previously-required 15 hours TIS inspection interval. This condition, if not corrected, could result in loose bearing attachment bolts, or cracked bearing supports, which could result in loss of drive to the tail rotor and subsequent loss of control of the helicopter.
	The Luftfahrt-Bundesamt (LBA), which is the airworthiness authority for the Federal Republic of Germany, recently notified the FAA that an unsafe condition may exist on Eurocopter Deutschland GmbH (ECD) Model EC 135 helicopters.  The LBA advises that loosening of bolt connections at bearing supports may lead to a tail rotor failure and thus to the loss of the helicopter.  The LBA issued AD 1998-033/6, dated July 9, 1998, applicable to ECD Model EC 135 helicopters.
	The FAA has reviewed Eurocopter EC 135 Alert Service Bulletin No. EC 135-53A-002, Revision 1, dated July 7, 1998, which describes procedures for visually inspecting the bearing supports, and Eurocopter EC 135 Alert Service Bulletin No. EC 135-53A-005, Revision 1, dated April 6, 1998, which describes procedures for measuring vibrations on the tail rotor drive shaft and replacement of roller bearing attaching hardware at bearing locations.
	This helicopter model is manufactured in the Federal Republic of Germany and is type certificated for operation in the United States under the provision of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement.  Pursuant to this bilateral airworthiness agreement, the LBA has kept the FAA informed of the situation described above.  The FAA has examined the findings of the LBA, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operations in the United States.
	Since an unsafe condition has been identified that is likely to exist or develop on other Eurocopter Deutschland GmbH Model EC 135 helicopters of the same type design, this AD requires, before further flight, a tail rotor drive shaft vibration survey and installation of a Fenestron Shaft Retrofit Kit L 535M3002 882. Also, before further flight, and thereafter at intervals not to exceed 15 hours TIS, the AD requires inspecting the bearing attaching lock plates at each bearing support for bent-open tabs, and inspecting for broken or missing slippage marks.  If a bearing attaching lock plate tab is bent open, or if a slippage mark is broken or missing, the FAA must be notified.  Finally, the AD requires, before further flight, and thereafter at intervals not to exceed 3 hours TIS, inspecting the bearing supports for cracks in the areas shown in the attached Figure 1, from the bend radius to the attaching screws and rivets connecting the bearing supports to the tailboom.  Use of a 6-power or higher magnifying glass and a bright light are required for this inspection.  If a crack is found, the bearing supports are to be replaced with airworthy bearing supports.
	This rule is issued under 49 U.S.C. Section 44701 pursuant to the authority delegated to me by the Administrator, and is effective immediately upon receipt of this priority letter.

98-15-25  EUROCOPTER DEUTSCHLAND GmbH:  Docket No. 98-SW-35-AD.  Supersedes AD 98-09-11, Amendment 39-10632, Docket No. 98-SW-18-AD.

	Applicability:  Model EC 135 helicopters, certificated in any category.

	NOTE 1:  This AD applies to each helicopter 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 helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (d) to request approval from the FAA.  This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD.  Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD.  In no case does the presence of any modification, alteration, or repair remove any helicopter from the applicability of this AD.

	Compliance: Required as indicated, unless accomplished previously.
	To detect loose tail rotor drive shaft bearing (bearing) attachment bolts, or cracked bearing supports, which could result in loss of drive to the tail rotor and subsequent loss of control of the helicopter, accomplish the following:
	(a)	Before further flight, conduct a tail rotor drive shaft vibration survey and install a Fenestron Shaft Retrofit Kit L 535M3002 882.
	(b)	Before further flight, and thereafter at intervals not to exceed 15 hours time-in-service (TIS), at each bearing support:
		(1)	Inspect each bearing attaching lock plate that was installed with the Fenestron Shaft Retrofit Kit L 535M3002 882 for bent-open tabs.
		(2)	Inspect for broken or missing slippage marks that may indicate looseness or rotation of attaching hardware.
		(3)	If a lock plate tab is bent open on bearing supports A, B, or C (shown in Figure 1), or if slippage marks are broken or missing, contact the Manager, Rotorcraft Standards Staff, FAA, telephone (817) 222-5110, fax (817) 222-5961.
	(c)	Before further flight, and thereafter at intervals not to exceed 3 hours TIS, using a 6-power or higher magnifying glass and a bright light, visually inspect bearing supports B and C as shown in Figure 1, from the bend radius to the attaching screws and rivets connecting the bearing supports to the tailboom.  If a crack is found, replace the bearing support with an airworthy bearing support.
	(d)	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, Rotorcraft Standards Staff, FAA.  Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Rotorcraft Standards Staff.

	NOTE 2:  Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Rotorcraft Standards Staff.

	(e)	Special flight permits will not be issued.

	NOTE 3:  The subject of this AD is addressed in Luftfahrt-Bundesamt (Federal Republic of Germany) AD 1998-033/6, dated July 9, 1998.  

	(f)	Priority Letter AD 98-15-25, issued July 17, 1998, becomes effective upon receipt.

FOR FURTHER INFORMATION CONTACT:  Mr. Scott Horn, Aerospace Engineer, FAA, Rotorcraft Directorate, Rotorcraft Standards Staff, 2601 Meacham Blvd., Fort Worth, Texas 76137, telephone (817) 222-5125, fax (817) 222-5961.