Aviation safety issues and actions

Inspection period for blade cracking

Issue number: AO-2017-066-SI-02
Who it affects: Air transport operators whose aircraft are fitted with Trent 700 engines.
Issue owner: Rolls-Royce plc
Transport function: Aviation: Air transport
Background: Investigation Report AO-2017-066
Issue release date: 30 June 2020
Current issue status: Closed – Adequately addressed
Issue status justification:

The likelihood of further fan blade failures has been reduced due to the actions taken by the engine manufacturer, including the enhanced inspection technique with smaller intervals, and the removal of the blades that have an increased probability of failure through stress induced cracking.

Safety issue description

The scheduled inspections recommended by Rolls-Royce to detect cracking in Trent 700 fan blades, were insufficient to detect early onset fatigue cracks in the membrane to panel bond before those cracks could progress to failure.

Proactive action

Action number: AO-2017-066-NSA-039
Action organisation: Rolls-Royce plc
Date: 30 June 2020
Action status: Closed

Rolls-Royce has taken the following safety actions to manage the risk of in-service fan blade cracking:

  1. 211-72-AH465 Revision 4 was issued on 3 October 2017 to reduce the initial and repeat inspection threshold from 2,400 cycles to 1,200 cycles. An alleviation period was included for Trent 700 low-pressure (LP) compressor (fan) blades that were affected by this change.
  2. On 26 July 2018, Rolls-Royce issued Revision 5 to Service Bulletin RB.211-72-AH465 to specify the requirements for operators conducting standard and non-standard operations (as defined in Time Limits Manual, 05-00-01). Additional changes were also made to the compliance section, to ensure all blades were inspected at an interval of 1,200 cycles by 31 December 2018.
  3. On 9 August 2018, Rolls-Royce issued a non-modification service bulletin RB211-72-K096. This service bulletin recommended the removal and re‑inspection of specific serial number LP compressor (fan) blades where indications were identified at earlier inspections, but were below the threshold for rejection.
  4. In November 2019, Rolls-Royce revised RB.211-72- AH465 (Revision 6) to introduce an enhanced inspection process thereby enabling the nominated inspection techniques to identify smaller cracks. Specifically, the revised water-coupled phased-array inspection has been shown to be a more reliable and repeatable technique whilst increasing detection sensitivity to identify smaller defects. The service bulletin also introduced improvements to the C-scan post-processing software and provided additional compliance limitations.
  5. In addition, Rolls-Royce explored ways to better mitigate the effect of imbalance and vibrational loads following a fan blade failure event. The result was a control system modification, designed to shut the engine down quickly when fan blade failure event occurs to reduce damage to the LP (fan) shaft. This control system modification, RB.211-73-J947 RB 73-J947, will be installed on the Electronic Engine Controller (EEC) during its next scheduled maintenance visit.

Proactive action

Action number: AO-2017-066-NSA-040
Action organisation: European Aviation Safety Agency
Date: 30 June 2020
Action status: Closed

On 5 September 2018, the European Aviation Safety Agency (EASA) issued Airworthiness Directive (AD) 2018-0188R1 for the inspection/replacement of Trent 700 engine low pressure compressor (fan) blades. The AD was a revision to an earlier AD, with the updated requirements per the most recent Rolls-Royce NMSB RB.211-72-AH465.

Last update 30 June 2020