The US FAA on 9 November will issue final airworthiness directives that require operators of 380 US-registered Bombardier CRJ700 and CRJ900 regional jets and 44 Airbus A330 aircraft to inspect for and possibly replace defective angle-of-attack sensors or components.
The directives follow nearly identical angle-of-attach (AOA) mandates issued by the European Aviation Safety Agency for the CRJ700/900 and Airbus A330/A340 last year and earlier this year, respectively. The FAA mandate also applies to A340s, though there are currently no A340s registered to US operators.
At issue is the manufacturing of the position transducers that convert physical AOA vane position to an electronic equivalent. An investigation by Thales revealed that oil residue between the rotor and stator portions of the resolver, mistakenly left in place during manufacturing, become viscous at low temperatures, typically in cruise, can cause a lag in vane movement.
"Such a condition could lead to discrepant AOA measurement. If not corrected, and if two or three AOA probes were simultaneously affected and provided wrong indications of the AOA to a similar extent, it could lead to a late activation of the [AOA] protection, which in combination with a high angle of attack would constitute an unsafe condition," the FAA states for the A330/A340 AD.
For the CRJ700/900, the FAA says the problem could "result in early or late activation of the stick shaker and/or stick pusher".
Operators must check for faulty parts within 750h of the mid-December effective date of the rule for the CRJ aircraft, replacing faulty AOA transducers. For the A330/A340, operators must complete an inspection and AOA change out within three months of the effective date of the AD.
Source: Air Transport Intelligence news
