Provisional text

JUDGMENT OF THE COURT (Eighth Chamber)

13 June 2024 (*)

(Reference for a preliminary ruling – Air transport – Regulation (EC) No 261/2004 – Article 5(3) – Compensation for passengers in the event of long delay or cancellation of flights – Exemption from the obligation to pay compensation – Extraordinary circumstances – Reasonable preventive measures – Technical failures caused by a hidden design defect – Design defect affecting an aircraft engine – Obligation of the air carrier to have back-up aircraft)

In Case C‑411/23,

REQUEST for a preliminary ruling under Article 267 TFEU from the Sąd Okręgowy w Warszawie (Regional Court, Warsaw, Poland), made by decision of 26 May 2023, received at the Court on 3 July 2023, in the proceedings

D. S.A.

v

P. S.A.,

THE COURT (Eighth Chamber),

composed of N. Piçarra, President of the Chamber, N. Jääskinen and M. Gavalec (Rapporteur), Judges,

Advocate General: L. Medina,

Registrar: A. Calot Escobar,

having regard to the written procedure,

after considering the observations submitted on behalf of:

–        D. S.A., by P. Gad, K. Puchalska and K. Żbikowska, adwokaci,

–        P. S.A., by E. Cieplak-Greszta, adwokat,

–        the Polish Government, by B. Majczyna, acting as Agent,

–        the European Commission, by N. Yerrell and B. Sasinowska, acting as Agents,

having decided, after hearing the Advocate General, to proceed to judgment without an Opinion,

gives the following

Judgment

1        This request for a preliminary ruling concerns the interpretation of Article 5(3) of Regulation (EC) No 261/2004 of the European Parliament and of the Council of 11 February 2004 establishing common rules on compensation and assistance to passengers in the event of denied boarding and of cancellation or long delay of flights, and repealing Regulation (EEC) No 295/91 (OJ 2004 L 46, p. 1).

2        The request has been made in proceedings between D. S.A., formerly P.[R] (‘the applicant in the main proceedings’), the assignee of the rights of J.D., and P. S.A., an air carrier (‘the air carrier at issue in the main proceedings’), concerning the latter’s refusal to pay compensation to J.D., a passenger whose flight was subject to a long delay in arrival.

 Legal context

3        Recitals 1, 14 and 15 of Regulation No 261/2004 state:

‘(1)      Action by the [European] Community in the field of air transport should aim, among other things, at ensuring a high level of protection for passengers. Moreover, full account should be taken of the requirements of consumer protection in general.

…

(14)      As under the [Convention for the Unification of Certain Rules for International Carriage by Air, concluded in Montreal on 28 May 1999 and approved on behalf of the European Community by Council Decision 2001/539/EC of 5 April 2001 (OJ 2001 L 194, p. 38)], obligations on operating air carriers should be limited or excluded in cases where an event has been caused by extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken. Such circumstances may, in particular, occur in cases of political instability, meteorological conditions incompatible with the operation of the flight concerned, security risks, unexpected flight safety shortcomings and strikes that affect the operation of an operating air carrier.

(15)      Extraordinary circumstances should be deemed to exist where the impact of an air traffic management decision in relation to a particular aircraft on a particular day gives rise to a long delay, an overnight delay, or the cancellation of one or more flights by that aircraft, even though all reasonable measures had been taken by the air carrier concerned to avoid the delays or cancellations.’

4        Article 5 of that regulation, headed ‘Cancellation’, provides:

‘1.      In case of cancellation of a flight, the passengers concerned shall:

…

(c)      have the right to compensation by the operating air carrier in accordance with Article 7, unless [they are informed of the cancellation]:

…

3.      An operating air carrier shall not be obliged to pay compensation in accordance with Article 7, if it can prove that the cancellation is caused by extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken.

…’

5        Article 7 of Regulation No 261/2004, headed ‘Right to compensation’, provides, in paragraph 1:

‘Where reference is made to this Article, passengers shall receive compensation amounting to:

(a)      EUR 250 for all flights of 1 500 kilometres or less;

(b)      EUR 400 for all intra-Community flights of more than 1 500 kilometres, and for all other flights between 1 500 and 3 500 kilometres;

(c)      EUR 600 for all flights not falling under (a) or (b).

…’

 The dispute in the main proceedings and the questions referred for a preliminary ruling

6        On 2 July 2018, J.D. entered into a contract of air carriage with the air carrier at issue in the main proceedings concerning a flight from Cracow (Poland) to Chicago (United States).

7        Previously, in April 2018, the manufacturer of the engine fitted to the aircraft scheduled to operate that flight had sent that carrier an instruction and a report which disclosed the existence of a hidden design defect affecting the high pressure compressor blades of engines fitted to aircraft of the same model (‘the engine design defect’) and imposed a number of restrictions on the use of those aircraft. After that date, the carrier claims to have contacted various carriers on several occasions with a view to chartering additional aircraft to pre-empt the possibility of an engine design defect being discovered in any of the aircraft in its fleet.

8        On 28 June 2018, four days before the scheduled flight, an engine malfunction occurred during a flight operated by the aircraft scheduled to carry J.D. on the flight he had booked. In accordance with the recommendations of the engine manufacturer, the air carrier at issue in the main proceedings conducted an emergency inspection of the engine concerned and identified an engine design defect. After consulting the engine manufacturer, the engine concerned was taken out of service and was then disassembled and sent to a maintenance centre for repair. Since there were no immediately available spare engines due to a global engine shortage, it was not possible to replace the defective engine until 5 July 2018, so that the aircraft was brought back into service on 7 July 2018.

9        Against that background, the carrier operated the flight scheduled for 2 July 2018 that same day, but it did not use the aircraft initially earmarked for that flight, opting instead for a replacement aircraft which arrived more than three hours after the originally scheduled arrival time.

10      On 18 July 2018, J.D. assigned his claim arising from the long delay in the arrival of the flight to the applicant in the main proceedings.

11      Following the refusal of the air carrier at issue in the main proceedings to pay compensation in the amount of EUR 600 provided for in Article 7(1)(c) of Regulation No 261/2004, on the ground that the delay in the arrival of the flight concerned was due to the detection of a defect in the design of the aircraft engine and that it had taken all possible measures to minimise disruptions to the scheduled flight, the applicant in the main proceedings brought an action before the Sąd Rejonowy dla m. st. Warszawy w Warszawie (District Court, Warsaw, Poland) on 29 March 2019.

12      By its decision of 3 December 2021, that court of first instance held that the engine design defect discovered during the emergency inspection of 28 June 2018 constituted an ‘extraordinary circumstance’ within the meaning of Article 5(3) of Regulation No 261/2004 and that the air carrier at issue in the main proceedings had taken all reasonable measures possible to ensure that a replacement aircraft was available to operate the flight.

13      The applicant in the main proceedings brought an appeal against that decision before the Sąd Okręgowy w Warszawie (Regional Court, Warsaw, Poland), which is the referring court.

14      Although that court starts from the premiss that the delay to the flight concerned was due to the existence of an engine design defect, detected on 28 June 2018 during an emergency inspection of the aircraft concerned, it is uncertain on two counts.

15      In the first place, it wonders whether the engine design defect, which the engine manufacturer revealed to the air carrier concerned in April 2018 by sending the latter an instruction and a report imposing a number of restrictions on the use of the aircraft, may be covered by the concept of ‘extraordinary circumstances’ within the meaning of Article 5(3) of Regulation No 261/2004, as interpreted by the Court in its judgments of 22 December 2008, Wallentin-Hermann (C‑549/07, EU:C:2008:771); of 17 September 2015, van der Lans (C‑257/14, EU:C:2015:618); and of 12 March 2020, Finnair (C‑832/18, EU:C:2020:204), even though the occurrence of that defect had become foreseeable.

16      In that regard, the referring court has doubts as to whether the engine design defect would necessarily materialise, since the inspections carried out on the various aircraft had not revealed any fissures in the blade base. In addition, it draws attention to the fact that the engine manufacturer had not recommended the immediate grounding of all aircraft or stated that the aircraft were not airworthy.

17      In that context, the referring court also observes that air carriers must comply with particularly stringent technical and administrative procedures. Thus, an air carrier cannot claim, in principle, that it has no control over the occurrence of technical problems affecting the aircraft, whatever the cause, since it should follow all appropriate procedures or take all necessary, possible and reasonable measures to prevent the occurrence of an event liable to lead to the delay or cancellation of flights.

18      In the present case, according to the referring court, such procedures were complied with and the air carrier followed the recommendations of the engine manufacturer by carrying out inspections to the extent and with the frequency indicated. It could thus be argued that those inspections are inherent in the normal exercise of the carrier’s activity. The implementation of those procedures does not, however, mean that the air carrier has actual control over the discovery of the hidden design defect affecting the engine of the aircraft concerned.

19      In the second place, the referring court raises the question of the interpretation of the concept of ‘all reasonable measures’, within the meaning of Article 5(3) of Regulation No 261/2004, which an air carrier may be expected to take when confronted with ‘extraordinary circumstances’. In accordance with the case-law of the Court, since not all extraordinary circumstances confer exemption, the onus is still on the air carrier seeking to rely on them to establish that they could not on any view have been avoided by measures appropriate to the situation, namely by measures which, at the time those circumstances arise, meet conditions which are technically and economically viable for that carrier. The air carrier cannot be required to make sacrifices that are unbearable in the light of its capacities.

20      In that context, the referring court is unsure, in essence, about the extent of the ‘reasonable measures’ of a preventive nature which an air carrier could be expected to take in a situation in which the detection of a hidden design defect affecting one of its aircraft is uncertain. More specifically, while it doubts that the air carrier could be required, by way of those ‘reasonable measures’ of a preventive nature, to replace the engine before the design defect has actually been detected or to ground the aircraft until the engine manufacturer has corrected that defect, it does not rule out the possibility that the air carrier could be expected to draw up a plan to have a fleet of fully crewed aircraft ‘on standby’ to operate scheduled flights should extraordinary circumstances arise.

21      Lastly, the referring court states that, since April 2018, the air carrier concerned had contacted only 8 carriers with a view to chartering a replacement aircraft, which is insufficient in the view of the applicant in the main proceedings, which argues that the air carrier at issue in the main proceedings thus failed to contact 18 other air carriers, including those offering ‘wet lease’, namely the chartering of aircraft with crew. Furthermore, the applicant in the main proceedings observes that the steps taken by that carrier to charter a replacement aircraft were completed in September 2018, which shows that the carrier reacted belatedly to the likely occurrence of a design defect affecting the engine of one of its aircraft.

22      In those circumstances, the Sąd Okręgowy w Warszawie (Regional Court, Warsaw) decided to stay the proceedings and to refer the following questions to the Court of Justice for a preliminary ruling:

‘(1)      Does an engine design defect revealed by the manufacturer constitute an “extraordinary circumstance” and does it come within the scope of “unexpected [flight safety] shortcomings” within the meaning of recitals 14 and 15 of Regulation [No 261/2004], if the carrier knew about the potential design defect several months before the flight?

(2)      If the defect in the design of the engine referred to in [Question] 1 constitutes an “extraordinary circumstance” within the meaning of recitals 14 and 15 of Regulation [No 261/2004], do “all reasonable measures” as mentioned in recital 14 and in Article 5(3) of Regulation No 261/2004 refer to the expectation that the air carrier should take into account the likely revelation of a design defect in the aircraft engine and take preventive steps in order to have back-up aircraft at the ready for the purpose of Article 5(3) of Regulation No 261/2004 in order to relieve it of the obligation to pay the compensation provided for in Article 5(1)(c) and Article 7(1) of that regulation?’

 Consideration of the questions referred

 The first question

23      By its first question, the referring court asks, in essence, whether Article 5(3) of Regulation No 261/2004 must be interpreted as meaning that the detection of a hidden defect in the design of the engine of an aircraft which is to operate a flight is covered by the concept of ‘extraordinary circumstances’ within the meaning of that provision, even where the engine manufacturer had informed the air carrier of the existence of a defect of that kind several months before the flight concerned.

24      It should be recalled at the outset that passengers whose flights are delayed may be treated, for the purposes of the application of the right to compensation, as passengers whose flights are cancelled and they may thus rely on the right to compensation laid down in Article 7 of that regulation where they suffer, on account of a flight delay, a loss of time equal to or in excess of three hours, that is, where they reach their final destination three hours or more after the arrival time originally scheduled by the air carrier (see, to that effect, judgment of 19 November 2009, Sturgeon and Others, C‑402/07 and C‑432/07, EU:C:2009:716, paragraph 69).

25      Article 5(3) of that regulation, read in the light of recitals 14 and 15 thereof, releases an air carrier from that obligation to pay compensation if the carrier can prove that the cancellation or long delay in arrival is caused by ‘extraordinary circumstances’ which could not have been avoided even if all reasonable measures had been taken and, where such circumstances do arise, that it adopted measures appropriate to the situation, deploying all its resources in terms of staff or equipment and the financial means at its disposal, in order to prevent that situation from resulting in the cancellation or long delay of the flight in question (see, to that effect, judgment of 23 March 2021, Airhelp, C‑28/20, EU:C:2021:226, paragraph 22 and the case-law cited).

26      Since Article 5(3) constitutes a derogation from the principle that passengers are entitled to compensation, and given the objective pursued by Regulation No 261/2004, which is, as is apparent from recital 1 thereof, to ensure a high level of protection for passengers, the concept of ‘extraordinary circumstances’ within the meaning of Article 5(3) must be strictly interpreted (see, to that effect, judgment of 17 April 2018, Krüsemann and Others, C‑195/17, C‑197/17 to C‑203/17, C‑226/17, C‑228/17, C‑254/17, C‑274/17, C‑275/17, C‑278/17 to C‑286/17 and C‑290/17 to C‑292/17, EU:C:2018:258, paragraph 36 and the case-law cited).

27      In that regard, it should be borne in mind that the concept of ‘extraordinary circumstances’ within the meaning of Article 5(3) of Regulation No 261/2004 refers to events which, by their nature or origin, are not inherent in the normal exercise of the activity of the air carrier concerned and are beyond that carrier’s actual control; those two conditions are cumulative and their fulfilment must be assessed on a case-by-case basis (see, to that effect, judgment of 23 March 2021, Airhelp, C‑28/20, EU:C:2021:226, paragraph 23 and the case-law cited).

28      Thus, unless the two cumulative conditions referred to in the preceding paragraph are met, technical failures do not constitute in themselves ‘extraordinary circumstances’ within the meaning of Article 5(3) of Regulation No 261/2004 (see, to that effect, judgments of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 25, and of 12 March 2020, Finnair, C‑832/18, EU:C:2020:204, paragraph 39).

29      It is in that context that it is necessary to assess whether the detection of a hidden defect in the design of an aircraft engine resulting in a long delay in the arrival of a flight, where the air carrier had been informed of the existence of a defect of that kind by the engine manufacturer several months before that flight, is capable of constituting an ‘extraordinary circumstance’ within the meaning of Article 5(3) of Regulation No 261/2004.

30      In the first place, it must be determined whether a hidden design defect displaying the characteristics mentioned in the preceding paragraph is capable of constituting, by its nature or origin, an event which is not inherent in the normal exercise of the activity of the air carrier.

31      In that regard, the Court has held that, in the light of the specific conditions in which carriage by air takes place and the degree of technological sophistication of aircraft, since the functioning of aircraft inevitably gives rise to technical problems, breakdowns or the premature and unexpected failure of certain aircraft parts, air carriers are confronted as a matter of course in the exercise of their activity with such problems (see, to that effect, judgment of 4 April 2019, Germanwings, C‑501/17, EU:C:2019:288, paragraph 22 and the case-law cited).

32      It follows therefrom that the resolution of a technical problem caused by a breakdown, a failure to maintain an aircraft or the premature and unexpected failure of certain aircraft parts is considered to be inherent in the normal exercise of the activity of the air carrier (see, to that effect, judgments of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 25; of 17 September 2015, van der Lans, C‑257/14, EU:C:2015:618, paragraphs 41 and 42; and of 12 March 2020, Finnair, C‑832/18, EU:C:2020:204, paragraph 41).

33      However, technical failures in a situation in which the manufacturer of the aircraft comprising the fleet of the air carrier concerned, or a competent authority, reveals, after those aircraft entered into service, that the aircraft are affected by a hidden manufacturing defect impinging on flight safety, are not inherent in the normal exercise of the activity of the air carrier and, therefore, are capable of falling within the concept of ‘extraordinary circumstances’ (see, to that effect, judgments of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 26, and of 17 September 2015, van der Lans, C‑257/14, EU:C:2015:618, paragraph 38).

34      In the present case, as is apparent from the order for reference, it has been established that the aircraft initially earmarked to operate the delayed flight was affected by a hidden design defect concerning all engines of the same type and impinging on flight safety, a defect which was revealed by the engine manufacturer a few months before its detection in the aircraft concerned. In accordance with the case-law cited in the preceding paragraph, such an event is not inherent in the normal exercise of the activity of the air carrier.

35      In the second place, it is necessary to decide whether the detection of a hidden defect in the design of an engine displaying the characteristics referred to in paragraph 29 above must be regarded as constituting an event entirely beyond the actual control of the air carrier concerned, that is to say, an event over which the air carrier has no control (see, to that effect, judgment of 23 March 2021, Airhelp, C‑28/20, EU:C:2021:226, paragraph 36).

36      It is true that, as a matter of principle, technical failures or breakdowns are not beyond the actual control of the air carrier, since their prevention or repair are part of the responsibility that falls on that air carrier to ensure the maintenance and proper functioning of the aircraft it operates for business purposes (judgment of 17 September 2015, van der Lans, C‑257/14, EU:C:2015:618, paragraph 43). However, the situation is different in the case of a hidden defect in the design of an aircraft engine.

37      First, although it is for the air carrier to ensure the maintenance and proper functioning of the aircraft it operates for business purposes, it is questionable whether, where a hidden design defect is revealed by the manufacturer of the aircraft in question, by the engine manufacturer or by the competent authority only after that aircraft has entered into service, it actually falls within the remit of that carrier to identify and correct that defect, with the result that the carrier cannot be considered to exercise control over the occurrence of such a defect.

38      Secondly, it is apparent from the case-law of the Court relating to the concept of ‘extraordinary circumstances’ within the meaning of Article 5(3) of Regulation No 261/2004 that events whose origin is ‘internal’ must be distinguished from those whose origin is ‘external’ to the air carrier, and only the latter are capable of falling outside the actual control of that carrier. The concept of ‘events of external origin’ encompasses events which result from the activity of the air carrier and from external circumstances which are more or less frequent in practice but which the air carrier does not control because they arise from an act of a third party, such as another air carrier or a public or private operator interfering with flight or airport activity (judgment of 7 July 2022, SATA International – Azores Airlines (Failure of the refuelling system), C‑308/21, EU:C:2022:533, paragraph 25 and the case-law cited).

39      It is therefore necessary in the present case to determine whether the notification or recognition by the engine manufacturer, prior to the delayed flight in question, of the existence of a hidden defect in the design of an aircraft engine liable to impinge on flight safety is capable of constituting an act of a third party which affects the carrier’s air activity and, therefore, of constituting an event of external origin.

40      In that regard, it should be noted that it does not follow from the case-law cited in paragraphs 33 and 38 above that the Court makes the classification of a hidden design defect as an ‘extraordinary circumstance’ subject to the condition that the aircraft manufacturer, the engine manufacturer or the competent authority must have revealed the existence of that defect before the technical failure caused by that defect occurred. The point in time at which the link between the technical failure and the hidden design defect is revealed by the aircraft manufacturer, the engine manufacturer or the competent authority is irrelevant, since that defect existed at the time of the cancellation or long delay of the flight and the carrier had no means of control to correct it.

41      The classification of a situation such as that at issue in the main proceedings as an ‘extraordinary circumstance’ within the meaning of Article 5(3) of Regulation No 261/2004 is consistent with the objective of ensuring a high level of protection for air passengers pursued by that regulation, as recital 1 thereof makes clear. That objective means that air carriers must not be encouraged to refrain from taking the measures necessitated by such an incident by prioritising the maintaining of punctuality of their flights over the objective of safety (see, by analogy, judgments of 4 May 2017, Pešková and Peška, C‑315/15, EU:C:2017:342, paragraph 25, and of 4 April 2019, Germanwings, C‑501/17, EU:C:2019:288, paragraph 28).

42      In the light of the foregoing, the answer to the first question is that Article 5(3) of Regulation No 261/2004 must be interpreted as meaning that the detection of a hidden defect in the design of the engine of an aircraft which is to operate a flight is covered by the concept of ‘extraordinary circumstances’ within the meaning of that provision, even where the engine manufacturer had informed the air carrier of the existence of a defect of that kind several months before the flight concerned.

 The second question

43      By its second question, the referring court asks, in essence, whether Article 5(3) of Regulation No 261/2004 must be interpreted as meaning that an air carrier must, as part of ‘all [the] reasonable measures’ which it is required to take in order to prevent the occurrence and the consequences of an ‘extraordinary circumstance’ within the meaning of that provision, such as the detection of a hidden defect in the design of the engine of one of its aircraft, adopt a preventive measure consisting of having a back-up fleet of aircraft on standby.

44      As recalled in paragraph 25 above, where an ‘extraordinary circumstance’ within the meaning of Article 5(3) of Regulation No 261/2004 arises, the carrier is released from its obligation to pay passengers compensation under Article 7 of that regulation only if it is able to prove that it adopted measures appropriate to the situation, namely measures which, at the time those ‘extraordinary circumstances’ arise, meet, inter alia, conditions which are technically and economically viable for that carrier (see, to that effect, judgments of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 40, and of 4 April 2019, Germanwings, C‑501/17, EU:C:2019:288, paragraph 31).

45      That air carrier must establish that, even if it had deployed all its resources in terms of staff or equipment and the financial means at its disposal, it would clearly not have been able, unless it had made intolerable sacrifices in the light of the capacities of its undertaking at the relevant time, to prevent the extraordinary circumstances with which it was confronted from leading to the cancellation or long delay of the flight (see, to that effect, judgments of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 41, and of 4 May 2017, Pešková and Peška, C‑315/15, EU:C:2017:342, paragraph 29).

46      Thus, the Court has established an individualised and flexible concept of ‘reasonable measures’, leaving to the national court the task of assessing whether, in a given situation, the air carrier may be regarded as having taken measures appropriate to the situation, namely measures which were technically and economically feasible for that air carrier when the extraordinary circumstances arose (see, to that effect, judgments of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 42; of 12 May 2011, Eglītis and Ratnieks, C‑294/10, EU:C:2011:303, paragraph 30; and of 4 May 2017, Pešková and Peška, C‑315/15, EU:C:2017:342, paragraph 30).

47      It follows that Article 5(3) of Regulation No 261/2004 cannot be interpreted as requiring air carriers, in a general and indiscriminate manner, to adopt, as part of the ‘reasonable measures’ referred to in that provision, a given preventive measure, such as having a back-up fleet of aircraft and the corresponding crew on standby, where it has been informed of the existence of an engine design defect revealed by the engine manufacturer, in order to prevent extraordinary circumstances from arising and the consequences thereof.

48      That being so, in order to assess whether the air carrier has taken ‘all reasonable measures’ within the meaning of Article 5(3) of Regulation No 261/2004, it is for the referring court to carry out an overall assessment which takes account, first, of all the measures taken by the air carrier since becoming aware of the existence of an engine design defect revealed by the manufacturer of that engine in the light of all the measures which it could have taken to guard against the occurrence of such an extraordinary circumstance affecting one of its aircraft, and, secondly, of the steps taken by that carrier following the detection of that defect in one of the engines of the aircraft concerned in order to avoid the cancellation or long delay of the flight concerned.

49      In that regard, it should be recalled that compliance with the minimum rules on maintenance of an aircraft is not in itself sufficient to establish that an air carrier has taken ‘all reasonable measures’ within the meaning of that provision (see, to that effect, judgment of 22 December 2008, Wallentin-Hermann, C‑549/07, EU:C:2008:771, paragraph 43).

50      In that context, it is for the referring court to assess, in the light of the air carrier’s financial means and its resources in terms of equipment and staff, whether it was in a position to charter back-up aircraft under the different arrangements available, namely dry lease / wet lease, or whether it was able, in the light of those resources, to replace the engine as a preventive step as part of a repair plan or to ground the aircraft until the engine had been repaired or replaced by the manufacturer. To that end, the referring court must take into consideration the limited availability of spare engines in the context of a global engine shortage, as well as the time needed to fit the new engine from the date on which the design defect came to light.

51      Finally, in connection with that overall analysis, it should also be noted that, in principle, there is nothing to prevent an air carrier, which has been informed of the existence of an engine design defect and of the possibility of its materialising in one of the aircraft it operates, from being required, as a preventive measure, to have a back-up fleet of aircraft and the corresponding crew on standby, if that measure is viable for that carrier from a technical, economic and staffing perspective, which it is for the referring court to assess.

52      By contrast, all the ‘reasonable measures’ which an air carrier may be expected to take cannot include the measure proposed by D. in its written observations, consisting of requiring an air carrier automatically to resize its flight network in proportion to its operational capacity. Such a measure may involve, at the flight planning stage, the cancellation or long delay of numerous flights due to the hypothetical occurrence of a design defect which is such as to require the carrier to make intolerable sacrifices in the light of the capacities of its undertaking.

53      In the light of the foregoing, the answer to the second question is that Article 5(3) of Regulation No 261/2004 must be interpreted as meaning that an air carrier may, as part of ‘all [the] reasonable measures’ which it is required to take in order to prevent the occurrence and the consequences of an ‘extraordinary circumstance’ within the meaning of that provision, such as the detection of a hidden defect in the design of the engine of one of its aircraft, adopt a preventive measure consisting of having a back-up fleet of aircraft on standby, provided that that measure is technically and economically feasible in the light of the carrier’s capacities at the relevant time.

 Costs

54      Since these proceedings are, for the parties to the main proceedings, a step in the action pending before the referring court, the decision on costs is a matter for that court. Costs incurred in submitting observations to the Court, other than the costs of those parties, are not recoverable.

On those grounds, the Court (Eighth Chamber) hereby rules:

1.      Article 5(3) of Regulation (EC) No 261/2004 of the European Parliament and of the Council of 11 February 2004 establishing common rules on compensation and assistance to passengers in the event of denied boarding and of cancellation or long delay of flights, and repealing Regulation (EEC) No 295/91,

must be interpreted as meaning that the detection of a hidden defect in the design of the engine of an aircraft which is to operate a flight is covered by the concept of ‘extraordinary circumstances’ within the meaning of that provision, even where the engine manufacturer had informed the air carrier of the existence of a defect of that kind several months before the flight concerned.

2.      Article 5(3) of Regulation No 261/2004

must be interpreted as meaning that an air carrier may, as part of ‘all [the] reasonable measures’ which it is required to take in order to prevent the occurrence and the consequences of an ‘extraordinary circumstance’ within the meaning of that provision, such as the detection of a hidden defect in the design of the engine of one of its aircraft, adopt a preventive measure consisting of having a back-up fleet of aircraft on standby, provided that that measure is technically and economically feasible in the light of the carrier’s capacities at the relevant time.

[Signatures]

*      Language of the case: Polish.