Consultation expired with comments. The Proposed Deviation has been updated based on the comments received and the corresponding Comment-Response Document (CRD) has been completed by EASA.
Details
Identification of issue
CS-E 800(a) states the objective that the Engine will respond in a safe manner following specified encounters with birds, as part of compliance with CS-E 540.
CS-E 540(a) states that the strike and ingestion of foreign matter that is likely to affect only one Engine will not cause any Hazardous Engine Effects, except that events with a probability of occurrence lower than Extremely Remote need not be considered.
CS-E 540(b) states the safety objectives for strike and ingestion of foreign matter that is likely to affect more than one Engine. These objectives include the continued safe flight and landing of the aircraft as a consequence of a Hazardous Engine Effect or, among others, an unacceptable immediate or subsequent loss of performance.
As per Special Condition M-TS-000398 “Bird Strike and Ingestion – Bird orientation”, when evidence exists that an immediate IFSD or Hazardous Engine Effect could result from:
- the impact of a bird with a mass not greater than that considered in CS-E 800(c)(1)(iii), but with a bird yaw orientation to the engine centre line instead of an axial orientation as considered for initial demonstration of compliance with CS-E 800(c), OR
- the impact of a bird with a mass not greater than that considered in CS-E 800(d)(1) or (d)(3), but with a bird yaw orientation to the engine centre line instead of an axial orientation as considered for initial demonstration of compliance with CS-E 800(d),
then, in order to demonstrate compliance with CS-E 800(a), in addition to the specifications in CS-E 800(c) and/or CS-E 800(d), the demonstration of compliance must also require to re-evaluate compliance with CS-E 800(c) and/or CS-E 800(d), as applicable depending on the evidence above, but including the impact of any bird with any bird yaw orientation to the centre line, and with a modified acceptance criteria that the ingestion will not lead to an immediate IFSD or Hazardous Engine Effect.
Two known field events of medium bird ingestions and one event of large flocking bird ingestion have caused the fracture of a fan blade of turbofan engines near the root, followed by an IFSD, and in two events an under-cowl fire. In all cases the birds are assumed by the Applicant to have been presented to the engines in a 90-degree (yaw) orientation to the engine center line, claimed by the Applicant to be a more adverse orientation compared to one aligned axially with the centre line of the engine, as historically interpreted from CS-E 800.
During the compliance finding activities for the certification of new turbofan engine models, the design of the fan blade was identified as not compliant with CS-E 800(a) and with the Special Condition M-TS-000398 “Bird Strike and Ingestion – Bird orientation”.
Therefore, the Applicant has requested a deviation , and per point 21.B.80(a)3(i) of Part 21 the Applicant has proposed mitigation factors to demonstrate compliance with the applicable essential airworthiness requirements of Annex II to Regulation (EU) 2018/1139. EASA has accepted this request for a deviation.
