AD 99-17-07

AD 99-17-07 EUROCOPTER DEUTSCHLAND GMBH: Emergency priority letter issued August 6, 1999. Docket No. 99-SW-49-AD

Applicability: Model MBB-BK 117 A-1, A-3, A-4, B-1, B-2, and C-1 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 otherwise 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 request approval for an alternative method of compliance in accordance with paragraph (e) 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 previously accomplished.
To prevent main rotor blade (blade) separation due to failure of a tension-torsion (TT) strap, accomplish the following:

(a) Before further flight,
(1) Create a component log card or equivalent record for each TT strap.

(2) Review helicopter and each TT strap history. Determine the calendar age since initial installation on any helicopter and number of flights on each TT strap. Enter both the age and number of flights for each TT strap on the component log card or equivalent record. For time-in-service (TIS) where the number of flights is unknown, multiply the number of hours TIS by 5 to determine the number of flights.

(3) If the total TIS or number of flights and calendar age cannot be determined, the TT strap must be removed from service.

(4) Remove any TT strap from service that has either accumulated 25,000 or more flights or is 15 or more years of age.

(b) When a TT strap age exceeds 10 calendar years, reduce the allowable number of flights from the maximum of 25,000 flights by 3,000 for each year exceeding 10. Before further flight, remove the TT strap from service before exceeding the allowable number of flights or 15 calendar years, whichever occurs first.

(c) If a TT strap age exceeds 10 calendar years but does not exceed the allowable number of flights, inspect the TT strap in accordance with paragraph 2.B.2 of the "Accomplishment Instructions," Eurocopter Deutschland GMBH Alert Service Bulletin MBB-BK 117 No. ASB-MBB-BK 117-10-120 (ASB), according to the following:

TT strap calendar age greater than 10 years, inspect within the next 6 weeks.
TT strap calendar age greater than 11 years, inspect within the next 5 weeks.
TT strap calendar age greater than 12 years, inspect within the next 4 weeks.
TT strap calendar age greater than 13 years, inspect within the next 3 weeks.
TT strap calendar age greater than 14 years, inspect within the next 2 weeks.

(1) If a defect is found as a result of the inspection, remove the TT strap from service prior to further flight.

(2) If no defect is found as a result of the inspection, a maximum of 500 flights is permitted on a one-time basis provided the limits of paragraphs (a)(4) and (b) are not exceeded.

(d) TT straps, part number (P/N) 2604067 or J17322-1, are not eligible for installation. Prior to installation, P/N 2604067 or J17322-1 must be re-identified according to paragraph 2.B.1 of the "Accomplishment Instructions" of the ASB.

(e) 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.

(f) Special flight permits may be issued for up to five flights in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the helicopter to a location where the requirements of this AD can be accomplished.

(g) Copies of the applicable service information may be obtained from American Eurocopter Corporation, 2701 Forum Drive, Grand Prairie, Texas 75053-4005, telephone (972) 641-3460, fax (972) 641-3527. This information may be examined at the FAA, Office of the Regional Counsel, Southwest Region, 2601 Meacham Blvd., Room 663, Fort Worth, Texas.

NOTE 3: The subject of this AD is addressed in Luftfahrt-Bundesamt (LBA), Federal Republic of Germany, AD 1999-284, dated August 6, 1999.

(h) Emergency Priority Letter AD 99-17-07, issued August 6, 1999, becomes effective upon receipt.

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DATE: August 6, 1999
99-17-07
This Emergency Priority Letter Airworthiness Directive (AD) is prompted by an accident in which a main rotor blade (blade) separation occurred resulting in three fatalities. The cause of the blade separation was a tension-torsion (TT) strap rupture within the main rotor head. The cause of the TT strap rupture remains under investigation. This condition, if not corrected, could result in failure of a TT strap, loss of a blade, and subsequent loss of control of the helicopter.

The Luftfahrt-Bundesamt (LBA), the airworthiness authority for the Federal Republic of Germany, recently notified the FAA that an unsafe condition may exist on all Eurocopter Deutschland GMBH (ECD) Model MBB-BK 117 helicopters. The LBA issued AD 1999-284, dated August 6, 1999, applicable to all ECD Model MBB-BK 117 helicopters.

The FAA has reviewed ECD Alert Service Bulletin MBB-BK 117 No. ASB-MBB-BK 117-10-120, dated August 6, 1999 (ASB).The ASB describes procedures for determining the total accumulated installation time and number of flights on the TT strap. The ASB specifies either inspecting or replacing an unairworthy TT strap with an airworthy TT strap.

This helicopter model is manufactured in the 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 ECD Model MBB-BK 117 helicopters of the same type design, this AD requires, before further flight, creating a component log card or equivalent record and determining the calendar age and number of flights on the TT strap. The AD also requires inspecting and removing, as necessary, certain unairworthy TT straps. Certain TT straps are not eligible for installation until they are re-identified. The actions are required to be accomplished in accordance with the ASB described previously.

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 emergency airworthiness directive.