Applicability: Rolls Royce Model RB211-524 series engines, all marks, installed on Boeing 747 and 767 and Lockheed L1011 aeroplanes fitted with High Pressure (HP) Turbine discs only listed in Table 1 of this AD.

Table 1: Applicable HP Turbine Discs.

This AD does not apply to HP turbine discs, which are pre modification Service Bulletin (SB) 72-7730, post modification SB72-C109 or post modification SB72-C762.

Requirement: Carry out an eddy current inspection of the HP turbine disc in accordance with Section 3 - Accomplishment instructions of Rolls Royce NMSB 72-AE718 original issue or later EASA approved revision.
If a HP turbine disc has previously passed the inspection to Rolls-Royce NMSB 72-C816 or the focussed inspection carried out in accordance with Rolls-Royce TS594-J Overhaul Process Manual Task 70-00-00-200-223 at greater than 700 cycles since new, then either of these inspections meets the requirements of this AD. Note: UK CAA AD G-2006-0002 EASA approval No. 2006-0034 dated 25 January 2006 refers.

Compliance:

1. For all RB211-524 engine marks except RB211-524D4 variants:

(a) If the HP turbine disc cycles were greater than 6150 cycles since new on 24 November 2005, inspect the HP turbine disc within 500 cycles from 24 November.
(b) If the HP turbine disc cycles were less than 6150 cycles since new on 24 November 2005, inspect the disc by whichever is the soonest of the conditions below:
(i) Prior to reaching 6650 cycles since new. The HP turbine disc life at inspection must be greater than 700 cycles since new.
(ii) At next shop visit where the HP turbine rotor is removed from the Combustor Outer Case and the HP turbine disc life is greater than 700 cycles since new. If a HP turbine disc that meets these cyclic life criteria is currently at shop visit, and if, at the effective date of this Airworthiness Directive, it has not yet been reinstalled into the Combustion Outer Case, then the HP turbine disc must be inspected in accordance with the requirements of this Airworthiness Directive at the current shop visit.

2. For all RB211-524D4 engine mark variants:

(a) If the HP turbine disc cycles were greater than 5000 cycles since new on 24 November 2005, inspect the HP turbine disc within 500 cycles from 24 November 2005.
(b) If the HP turbine disc cycles were less than 5000 cycles since new on 24 November 2005, inspect the HP turbine disc by whichever is the soonest of the conditions below:
(i) Prior to reaching 5500 cycles since new. The HP turbine disc life at inspection must be greater than 700 cycles since new.
(ii) At the next shop visit where the HP turbine rotor is removed from the Combustor Outer Case and the HP turbine disc life is greater than 700 cycles since new. If a HP turbine disc that meets these cyclic life criteria is currently at shop visit, and if, at the effective date of this Airworthiness Directive, it has not yet been reinstalled into the Combustion Outer Case, then the HP turbine disc must be inspected in accordance with the requirements of this Airworthiness Directive at the current shop visit.

3. For all other HP turbine discs specified in the Applicability of this Directive but not listed in Table 2 of this AD:

Inspect the HP turbine disc at next shop visit where the HP turbine rotor is removed from the Combustor Outer Case and the HP turbine disc life is greater than 700 cycles since new. If a HP turbine disc that meets these cyclic life criteria is currently at shop visit; and if, at the effective date of this Airworthiness Directive, it has not yet been reinstalled into the Combustion Outer Case, then the HP turbine disc must be inspected in accordance with the requirements of this Airworthiness Directive at the current shop visit.

Table 2:

This Amendment becomes effective on 11 May 2006.

Background: A population of HP turbine discs that were manufactured between 1989-1999 and which were subject to possible machining anomalies, were believed to have an increased chance of suffering from cooling air hole cracking, compared to the general fleet population of HP turbine discs. As a result of this risk, Rolls-Royce issued Non-Modification Service Bulletin (NMSB) 72-C816, recommending in-service inspections of the subject discs. Recently an RB211 HP turbine disc has been found with a crack which had propagated further than expected from the risk model that was used to establish the original inspection defined in the above NMSB. This has led to the need for a revision of the original inspection requirements. An HP turbine disc fracture would be uncontained and create a potential unsafe condition. Accordingly, this AD introduces revised inspection requirements to reflect the increased risk of HP turbine disc cracking and potential disc fracture. This amendment corrects serial numbers and part numbers detailed in Table 1 and clarifies the compliance statements.

The original issue of this AD was to become effective on 11 May 2006.

FMI: www.casa.gov.au