AMC E 40(b)(3) and (b)(4) 30-Second OEI, 2-Minute OEI and 30-minute Power Ratings

ED Decision 2018/014/R

(1)     The 30-Second and 2-Minute OEI Power ratings are two separate ratings. However, they are associated in a combined structure of 2.5 minutes duration.

(2)     The 30-Second and 2-Minute OEI ratings are optional ratings that may be specifically requested by the applicant, and they are intended for use only for continuation of the one-flight operation after the Failure of one Engine in multi-engine Rotorcraft during take-off, climb or landing. The 30-Second OEI Power rating provides a short burst of power to complete the take-off or to effect a rejected take-off, should an Engine Failure occur at the critical decision point, so that the Rotorcraft can lift clear of any obstruction in the flight path and climb out or, alternatively, to reject the take-off. Similarly, this rating also provides adequate power for the Rotorcraft to execute a safe landing, or a baulked landing if an Engine fails at any point down to and including the landing decision point. The 2-Minute OEI Power rating provides a further period of increased power to enable the Rotorcraft to complete the climb out from take-off or baulked landing to safe altitude and airspeed.

(3)     While the 30-Second and 2-Minute OEI Power ratings were originally conceived as high power ratings, using the available margins in the Engine design, and followed by a mandatory Engine overhaul, the experience has shown that the manufacturers provide engines with differing capabilities and different margins. Therefore some flexibility is possible in defining the mandatory maintenance actions, provided they are appropriately validated during certification (see also AMC E 25).

(4)     These ratings have been intended for one usage per flight in an emergency during the take-off or landing phases. Nevertheless, the certification specifications have been defined around the worst-case scenario that involves the possible use of these ratings three times in one flight (i.e., the event at take-off, baulked landing and final landing). While it was not initially intended, it is recognised that these ratings could also be inadvertently used in some unexpected, non-critical conditions like an Engine Failure in a Rotorcraft flying at a high-speed cruise. In all cases, the required mandatory maintenance actions apply after any use of the rating powers.

(5)     In some circumstances, the highest power used during a 2.5-minute duration OEI event might be lower than the 30-Second OEI power band, but still within the certified power band of the 2-Minute OEI Power rating. In this case, it is permissible to extend the use of the 2-Minute OEI Power rating to a total duration of 2.5 minutes. However, that additional 30-Seconds period will be considered to be a derated 30-Second OEI Power rating. For the required mandatory maintenance actions, see CS-E 25(b)(2) and AMC E 25.

(6)     The 30-Second and 2-Minute OEI Power ratings should account for any deterioration observed during the applicable portion of the 2-hour additional endurance test of CS-E 740(c)(3)(iii).

Any available information from tests of CS-E 740(c)(3)(iii) may be used to establish the Engine characteristics throughout operating envelope of the Engine. In particular, the Power ratings for the 30-Second and 2-Minute OEI ratings should reflect the rated power deterioration that is observed during the pre-2-hour test calibration through and including the third application of 30-Second OEI rated power during the additional endurance test. The power deterioration through the third application is expected to be the best indicator of the worst case power deterioration that could occur during actual usage of the rating, and thus it should be reflected in the data given to the aircraft manufacturer to define the performance characteristics of the aircraft system. In the event of a power deterioration that exceeds 10% at the 30-Second OEI rating over the course of the 2-hour test, the mode of deterioration should be evaluated to ensure that the availability of 30-Second OEI rated power in service will not be compromised by any variability in the amount of deterioration.

(7)     For Rotorcraft turbine Engines, ‘Rated 30-Minute Power’ is the approved brake horsepower, developed under static conditions at specified altitudes and temperatures within the operating limitations established for the Engine, and limited in use for periods of no more than 30 minutes.

The 30-Minute Power rating may be set at any level between the Maximum Continuous up to and including the take-off rating, and may be used for multiple periods of up to 30 minutes each, at any time between the take-off and landing phases in any flight.

[Amdt No: E/1]

[Amdt No: E/5]