3 Even if the oil or gas temperature stabilization exception is justified, the acceleration and deceleration runs under § 33.87(b)(5) should still be completed in their entirety with rotor speeds and thrust or power at or above the 100 percent values to be certificated.
Additionally, the engine test configuration and the acceleration rate of the engine should remain the same as during the periods under §§ 33.87(b)(1) and (b)(2)(ii).
(5) Section 33.87(b)(6), Starts.
(a) The purpose of an engine start demonstration is to show that normal starts can be accomplished without exceeding the maximum starting temperature limit or causing engine hardware distress following:
1 A short period of engine shutdown, 2 An extended period of engine shutdown, 3 Minimum fuel drainage time or engine motoring time to purge accumulated fuel in the engine, or 4 A false start.
(b) The applicant must conduct 100 engine starts to satisfy the requirements under § 33.87(b)(6). The 100 starts consist of:
1 Twenty-five normal starts preceded by a minimum 2-hour shutdown.
2 At least 10 false engine starts, each time pausing for the applicant's specified minimum fuel drainage time before attempting a normal start. These starts are required to demonstrate the engine’s capability to purge unwanted fuel before energizing the ignition system.
3 At least 10 normal restarts preceded by a maximum 15-minute shutdown period.
4 Fifty-five additional normal starts if 10 false starts and 10 normal restarts are run. However, if more than 10 false starts and/or more than 10 normal restarts are run, there will be a lesser number of remaining normal starts.
(c) A normal start is measured from the initial indication of core rotor speed until stable ground idle speed (core rotor) is reached. The normal start should follow the ground start procedure as specified in the engine installation instructions.
(d) A false start is conducted as the engine motors on the starter for the maximum light-off time period, while leaving the igniter deactivated. At the end of this time period, the starter is then disengaged and the power lever is commanded to the fuel cutoff position. After the engine comes to a complete stop, a normal engine start is made. Prior to a normal start 22
attempt, the residual fuel in the engine may be purged by motoring the engine on the starter or draining the fuel as specified in the engine operating instructions. The maximum light-off time, maximum core rotor speed for starting, and minimum time required for motoring and fuel drainage used should adhere to the values specified in the installation instructions.
(e) The remaining starts in paragraph 3-4.b(5)(b)4 above should be preceded by shutdown periods that are greater than 15 minutes, but less than 2 hours. These starts may be completed anytime during and after the endurance test.
(f) After each of the starting demonstrations, the applicant should show that the engine can accomplish all subsequent normal starts without any abnormal indications, and without exceeding the maximum starting temperature limit specified in the engine installation or operating instructions.
(g) Any limitations associated with the normal start, such as the starting time or other engine operating parameters, should be specified in the TCDS and in the operating instructions manual as required by § 33.5(b)(3(i).
3-5. Endurance Test Schedule, § 33.87(c), for Rotorcraft Engines for which a 30-minute OEI Power Rating is Desired.
a. Guidance.
(1) This schedule is required for rotorcraft engines for which a 30-minute OEI power rating is desired. The schedule is the same as prescribed in § 33.87(b), except that the 1 hour and 30 minute test time in § 33.87(b)(3) at rated maximum continuous power is now split between 1 hour at maximum continuous power in § 33.87(c)(3) and 30 minutes at 30-minute OEI in § 33.87(c)(4). The test must include the sequential test runs defined in §§ 33.87(c)(1) through
(c)(7), unless we approve an alternative test sequence. Also, applicable to this test schedule is the guidance described in paragraph 3-4.a.(2) of this AC for required minimum physical power and the general endurance test requirements prescribed in § 33.87(a).
(2) The 150 hours of testing time consists of 13.75 hours at the takeoff power rating,
12.5 hours at the 30-minute OEI power rating, 37.5 hours at the maximum continuous power rating, 62.5 hours at the incremental power step time period, and 23.75 hours at the minimum idle condition.
(3) See figures 3 and 4 in appendix 1 of this AC for a graph representation of the § 33.87(c) test schedule.
b. Section 33.87(c)(1), Takeoff and idling. The guidance is identical to that provided for § 33.87(b)(1) under “Guidance” in paragraph 3-4.b.(1) of this AC.
c. Section 33.87(c)(2), Rated maximum continuous and takeoff power.
(1) In complying with this paragraph, the applicant should run the first 15 of 25 cycles for 30 minutes each at the rated maximum continuous power, and run the remaining 10 cycles for 30 minutes each at the rated takeoff power.
(2) The applicant should maintain all limit parameters (rated power and associated maximum permissible torque, rotor speed, and gas temperature) for 30 minutes at the limit levels (redlines) associated with the rated maximum continuous or rated takeoff.
d. Section 33.87(c)(3), Rated maximum continuous power.
(1) In complying with this paragraph, the applicant should run 25 endurance test cycles at rated maximum continuous power for one hour each after completing the test sequence at rated maximum continuous and takeoff power of § 33.87(c)(2).
(2) The applicant should maintain all limit parameters (rated power and associated maximum permissible torque, rotor speed, and gas temperature) at maximum continuous rating power values for one hour.
e. Section 33.87(c)(4), Rated 30-minute OEI power.
(1) In complying with this paragraph, the applicant should run 25 endurance test cycles at rated 30-minute OEI power for 30 minutes each after completing the test sequence at rated maximum continuous power of § 33.87(c)(3).
(2) The acceleration should start from maximum continuous power and the deceleration should return to minimum idle power after this test sequence. The applicant should maintain all limit parameters (rated power and associated maximum permissible torque, rotor speed, and gas temperature) at 30-minute OEI rating redline values for 30 minutes at the rating.
f. Sections 33.87(c)(5), Incremental cruise power or thrust, § 33.87(c)(6) Acceleration and deceleration runs, and § 33.87(c)(7), Starts. The guidance for these three sections is identical to that described in paragraphs 3-4.b.(3), (4), and (5) for the requirements in §§ 33.87(b)(4), (b)(5), and (b)(6) respectively.
3-6. Endurance Test Schedule, § 33.87(d), for Rotorcraft Engines for which a Continuous OEI Rating is Desired.
a. Guidance.
(1) This test schedule is required for rotorcraft engines for which the applicant desires a continuous OEI power rating. The schedule is the same as § 33.87(b), except that a 1-hour test run at continuous OEI rating power replaces the one hour of maximum continuous time in each of the test runs under § 33.87(b)(3). The test must include the sequential runs in §§ 33.87(d)(1) through (d)(6) sequence unless we approve a different test sequence. Also, applicable to this test schedule is the guidance described in paragraph 3-4.a.(2) of this AC for the required minimum physical power and the general endurance test requirements prescribed in § 33.87(a).
(2) The 150 hours of testing time will consists of 18.75 hours at the takeoff rating, 25 hours at the continuous OEI rating, 20 hours at the maximum continuous rating, 62.5 hours at the incremental power step time, and 23.75 hours at the minimum idle condition.
(3) See figures 5 and 6 in appendix 1 of this AC for a graph representation of the § 33.87(d) test schedule.
b. Section 33.87(d)(1), Takeoff and idling, and § 33.87(d)(2), Rated maximum continuous and takeoff power. The guidance is the same as that described under “Guidance” in paragraph 3
4.b.(1) of this AC for § 33.87(b)(1) and paragraph 3-4.b.(2) of this AC for § 33.87(b)(2).
c. Section 33.87(d)(3), Rated continuous OEI power.
(1) In complying with this paragraph, the applicant must run 15 of the 25 endurance test cycles at rated continuous OEI power for one hour each after completing the test sequence under § 33.87(d)(2)(i) at rated maximum continuous power. The applicant must run 10 of the 25 endurance test cycles at rated continuous OEI power for one hour each after completing the test sequence under § 33.87(d)(2)(ii) at rated takeoff power.
(2) The applicant must maintain all limit parameters (rated power and associated maximum permissible torque, rotor speed, and gas temperature) for one hour at the maximum continuous OEI power.
d. Section 33.87(d)(4), Rated maximum continuous power.
(1) In complying with this paragraph, the applicant must run 25 endurance test cycles at rated maximum continuous power for one hour each after completing the test sequence at rated continuous OEI rating power of § 33.87(d)(3).
(2) The applicant must maintain all limit parameters (rated power and associated maximum permissible torque, rotor speed, and gas temperature) for one hour at the rated maximum continuous power.
e. Section 33.87(d)(5), Incremental cruise power, § 33.87(d)(6), Acceleration and deceleration runs, and § 33.87(d)(7), Starts. The guidance for these three sections is identical to that described in paragraphs 3-4.b.(3), (4), and (5) of this AC for the requirements in §§ 33.87(b)(4), (b)(5), and (b)(6) respectively, except that the run time, and the speed and time increments are 2 hours and not less than 12 increments, instead of the 2.5 hours and 15 increments under § 33.87(b)(4).
3-7. Endurance Test Schedule, § 33.87(e), for Rotorcraft Engines for which a 2½-minute OEI Power Rating is Desired.
a. Explanation.
(1) The maximum gross weight of a multiengine rotorcraft is limited by the power available from the remaining operating engine(s) when one engine fails or is shutdown during flight. Flight performance analysis has shown that in the event of engine failure at the critical point during take-off or landing, a period of higher power, referred to as 2½-minute OEI power, is required to lift the aircraft, gain forward speed, clear obstructions in the flight path, and climb to a safe altitude.
(2) Once the aircraft has reached a safe altitude, a longer period at a lower power, which is equal to or higher than maximum continuous power, is required to continue the fight until able to reach a suitable landing site. This power level will be rated maximum continuous, 30-minute OEI, or continuous OEI power depending on the rating structure of the engine. For these reasons, the endurance test schedules for the 2½-minute OEI rating are structured to run under one of the following three combinations of ratings:
(a) Rated takeoff, maximum continuous, and 2½-minute OEI, or
(b) Rated takeoff, maximum continuous, 2½-minute OEI, and 30-minute OEI, or
(c) Rated takeoff, maximum continuous, 2½-minute OEI, and continuous OEI.
(3) See appendix 9 of this AC for more information on rotorcraft operation at the 2½ minute OEI condition.
(4) The schedules prescribed in §§ 33.87(e)(1) and (e)(2) are required for rotorcraft engines for which the applicant desires a 2½-minute OEI power rating. The applicant should select one of the three combinations of ratings in paragraphs 3-7.a.(2)(a), (2)(b) and (2)(c) above for the engine model being certified and apply the associated test schedules for compliance with endurance test requirements.
(5) See figures 7 through 11 in appendix 1 of this AC for a graph representation of the § 33.87(e) test schedules.
b. Guidance. The test must include the runs specified in §§ 33.87(e)(1) and (e)(2), unless we approve an alternate test sequence. The guidance described in paragraphs 3-4.a.(2) of this AC for the required minimum physical power and the general endurance test requirements prescribed in § 33.87(a), apply to this test schedule.
(1) Section 33.87(e)(1), Takeoff, 2½-minute OEI and idling. This guidance is the same as that given for § 33.87(b)(1) under “Guidance” in paragraph 3-4.b.(1), except that during the third and sixth takeoff power periods in each of the alternate 5-minute periods, only 2.5 minutes 26
need be conducted at rated takeoff power. The applicant should conduct the remaining 2.5 minutes at rated 2½-minute OEI power.
(2) Section 33.87(e)(2). In complying with this paragraph, the applicant should select one of the options in the following paragraphs, depending on the rating structure of the engine:
(a) For engines with rated takeoff, maximum continuous, and 2½-minute OEI power ratings, the guidance is the same as that given for §§ 33.87(b)(2) through (b)(6) under “Guidance” in paragraphs 3-4.b.(2) through b.(5) of this AC, except that in the last one of the 25 endurance test cycles under § 33.87(b)(2)(ii), the last 5 minutes must be run at 2½-minute OEI power rating.
(b) For engines with rated takeoff, maximum continuous, 2½-minute OEI, and 30-minute OEI ratings, the guidance is the same as that given for § 33.87(c)(2) through (c)(7) in paragraphs 3-5.c through 3-5.f of this AC, except that, during the last of the 25 endurance test cycles, the last 5 minutes of § 33.87(c)(4) 30 minutes run at the 30-minute OEI power must be run at the 2½-minute OEI power.
(c) For engines with rated takeoff, maximum continuous, 2½-minute OEI, and continuous OEI ratings, the guidance is the same as that given for § 33.87(d)(2) through (d)(7) described in paragraphs 3-6.b through 3-6.e of this AC, except that during the last of the 25 endurance test cycles, the last 5 minutes of § 33.87(d)(4) one hour run at continuous OEI must be run at 2½-minute OEI power rating.
(d) See appendix 10 of this AC for the accumulated testing times for 150 hours of testing to these three schedules.
3-8. Endurance Test Schedule, § 33.87(f), for Rotorcraft Engines for which 30-second OEI and 2-minute OEI Ratings are Desired.
a. The 30-second OEI and 2-minute OEI power ratings. When used in combination, t he 30-second OEI and 2-minute OEI power ratings enable rotorcraft to perform a mission very similar to that of the 2½-minute OEI power rating described in section 3-7.a, “Explanation,” of this AC. There are, however, significant differences between these ratings.
(1) The use of the 2½-minute OEI rating is not limited to a certain number of occurrences, while the use of the 30-second OEI and 2-minute OEI ratings is limited to three occurrences during a single flight. In service, use of the 30-second OEI and 2-minute OEI ratings is likely once per flight with a required mandatory inspection after that flight. However, we have defined certification requirements around the worst-case scenario involving the possible use of the rating three times in one flight; takeoff, balked landing, and final landing of a rotorcraft. The intent of the 30-second OEI and 2-minute OEI ratings is to safely use available engine design margins for brief periods of exposure.
(2) Inspection and maintenance actions are not required after a flight when the 2½-minute OEI rating is used. Inspection and maintenance actions, however, are required after a 27
flight when either the 30-second OEI or the 2-minute OEI rating is used. This difference is supported by the pass or fail criteria of the teardown inspection requirements in § 33.93.
Following the endurance test for the engine’s 2½-minute OEI rating, the teardown inspection must show that all engine parts are in a condition for safe operation in compliance with § 33.93(a)(2). Following the endurance test for the engine’s 30-second OEI and 2-minute OEI ratings, the teardown inspection must show that the engine maintains its structural integrity in compliance with § 33.93(b)(2). Note that use of the 30-second OEI and 2-minute OEI ratings may result in component or part deterioration beyond serviceable limits, making these components unavailable for further use. See appendix 9 of this AC for more information on use of 30-second OEI and 2-minute OEI ratings for rotorcraft.
b. Endurance test for 30-second and 2-minute OEI ratings. The endurance test comprises of the 150 hour test run under §§ 33.87(b), (c), (d), or (e), as applicable to the engine OEI ratings structure, followed by a supplementary 2-hour test under § 33.87(f). See figures 12 and 13 in appendix 1 of this AC for graph representations of the § 33.87(f) test schedules.
(1) Following the tests in § 33.87(b), (c), (d), or (e), the applicant may disassemble the tested engine to the extent necessary to show compliance with the requirements of § 33.93(a).
The applicant must then reassemble the tested engine using the same engine parts used for the 150-hour endurance test run under §§ 33.87(b), (c), (d), or (e), except for those parts that are defined as consumable in the ICA. The level of component cleaning to facilitate the inspection prior to rebuild for the test under § 33.87(f) should be acceptable to us. The applicant should show that any cleaning during the teardown inspection, or replacement of consumable parts, will not enhance the engine’s ability to meet the requirements under § 33.93(b).
(2) The applicant may elect to continue the 2-hour test under § 33.87(f) without an intervening disassembly and inspection. In this case, the applicant must show that, after the test, the condition of engine parts and components comply with § 33.93(a) instead of § 33.93(b).
c. Test conduct. All requirements under § 33.87(a) apply to the conduct of the 2-hour test, except as permitted by § 33.87(f) and as discussed further in this section. The required minimum physical power and general endurance test requirements described in section 3-4.a, “Explanation,” of this AC for § 33.87(b) apply to this test schedule. In changing the power setting at the beginning and the end of each test sequence, the applicant should move the power control lever from one position to the other in no more than one second.
d. Test sequences.
(1) The applicant must conduct the prescribed 2-hour test sequence specified in §§ 33.87(f)(1) through (f)(8) a total of four times as follows:
(a) Three minutes at rated takeoff power;
(b) Thirty seconds at rated 30-second OEI power;
(c) Two minutes at rated 2-minute OEI power;
(d) Five minutes at whichever is the greatest of rated 30-minute OEI power, rated continuous OEI power, or rated maximum continuous power, except that this period must be 65 minutes during the first test sequence. However, where the greatest rated power is 30-minute OEI power, that 65-minute period must consist of 30 minutes at 30-minute OEI power followed by 35 minutes at continuous OEI power or maximum continuous power, whichever is greater;
(e) One minute at 50 percent takeoff power;
(f) Thirty seconds at rated 30-second OEI power;
(g) Two minutes at rated 2-minute OEI power; and
(h) One minute at minimum flight idle condition.
(2) The applicant must run the test sequences in §§ 33.87(f)(1) through (f)(8) four times, continuously and without stopping. In the event of a stoppage, the applicant should repeat the interrupted sequence in full, or the sequence may be restarted from the interruption point if there are technical justifications acceptable to us. If we determine that the sequence does not need to be repeated in its entirety, the applicant should restart the test from a point where the engine thermal condition would be the same as at the time of interruption. If we determine that the number of interruptions is excessive, the applicant should repeat the entire test under § 33.87(f).
e. Test time. The accumulated time of two hours of testing is split among four test sequences. The total duration of the first sequence is 75 minutes, while the duration for sequences 2, 3, and 4 is 15 minutes each. The time difference between these sequences is a result of the requirements under 33.87(f)(4). These requirements also dictate different test schedules for the first sequence depending on the other ratings that the certification engine has.
The intent of the power level of test condition under § 33.87(f)(4) is to demonstrate the highest en route OEI or non-OEI power. The following are test time breakdowns among the four sequences accounting for different engine ratings scenarios (see tables 1 and 2 below).
(1) Test time breakdown when (a) the engine does not have a 30-minute OEI rating, or
(b) the 30-minute OEI rating is less than either the continuous OEI, or the maximum continuous ratings, or both (see table 1).
Table 1.
Sequence 1
33.87 section Takeoff (minutes) 30-sec OEI (minutes) 2-min OEI (minutes) Flight idle (minutes) Greatest of continuous OEI or maximum continuous (minutes) 50% takeoff (minutes) f(1) 3 f(2) 0.5 f(3) 2 f(4) 65 f(5) 1 f(6) 0.5 f(7) 2 f(8) 1 Sequences 2, 3, and 4 f(1) 3 f(2) 0.5 f(3) 2 f(4) 5 f(5) 1 f(6) 0.5 f(7) 2 f(8) 1 Total test time (min) 12 4 16 4 80 4
(2) Test time breakdown when the 30-minute OEI r ating is greater than both the co ntinuous OEI and the maximum continuous ratings (see tab le 2).
Table 2.
Sequence 1
33.87 section Takeoff (minutes) 30-sec OEI (minutes) 2-min OEI (minutes) Flight idle (minutes) 30-min OEI (minutes) Greatest of Continuous OEI or maximum continuous (minutes) 50% takeoff (minutes) f(1) 3 f(2) 0.5 f(3) 2 f(4) 30 35 f(5) 1 f(6) 0.5 f(7) 2 f(8) 1 Sequences 2, 3, and 4 f(1) 3 f(2) 0.5 f(3) 2 f(4) 5 f(5) 1 f(6) 0.5 f(7) 2 f(8) 1 Total test time (min) 12 4 16 4 30 50 4
f. Air bleed during test. During the test in § 33.87(f), maximum air bleed for engine and aircraft services under § 33.87(a)(5) do not need to be used if the applicant can show by test, or analysis based on testing, that the engine’s ability to meet the teardown inspection requirements of § 33.93 is not enhanced. We permit this exception to reduce test complexity and improve the flexibility needed to attain key parameters during the test (rotational speed, temperature and torque). The analysis should include:
(1) The effect of the bleed air extraction on the engine secondary air system which provides cooling air to various engine components, and
(2) The thermodynamic cycle effects of bleed (for example, core speed to output shaft speed changes).
g. Accessory drives and mounting attachments. If, during testing the accessory drives and mounting attachments are not loaded, the applicant must add the equivalent power extraction to 31
the engine shaft output drive, as required under § 33.87(a)(6)(iii). This is so that the power turbine rotor assembly is operated at or above the same levels as if the accessory drives and mounting attachments were loaded.
h. Engine operating limitations. The engine operating limitations of the 30-second and 2-minute OEI ratings should be based on the minimum values obtained during the application of the 2-hour test under § 33.87(f). Further, the applicant should identify the limitations in the TCDS. The applicant should also account for stabilization time, instrumentation range of accuracy, and automatic controls features declared under §§ 33.29(c) and 33.28(k).
3-9. Endurance Test Schedule, § 33.87(g), Supersonic Aircraft Engines. We may address the test requirements of supersonic aircraft engines in a future AC.
3-10. Endurance Test Schedule, § 33.84, Engine Overtorque Test.
a. Maximum engine overtorque test, § 33.84. These requirements apply to turbopropeller and turboshaft engines that incorporate a free power turbine. The test requirements may be addressed as part of the endurance test of §§ 33.87(b), (c), (d), or (e). This guidance only applies when maximum engine overtorque testing is incorporated in the endurance test schedule of § 33.87. This guidance does not address the alternative tests available under § 33.84(a)(1).
b. Maximum engine overtorque. The maximum engine overtorque is permitted for all engine ratings, except for the 30-second and 2-minute OEI ratings, as stated by § 1.1, General definitions.
(1) The maximum engine overtorque is an "over the limit'' condition that could last up to 20 seconds, and which occurs inadvertently. After this condition occurs, the engine must remain operational without any maintenance action other than to correct the cause. The applicant should identify the failure modes that could produce engine overtorque conditions. For example, sudden changes in the rotorcraft or aircraft blade pitch or power demand, such as an engine failure on a twin engine rotorcraft, can cause a significant decrease in the rotor or propeller speed.
(2) When overtorque conditions may occur in association with more than a single rating, the applicant should declare the highest torque value as the maximum engine overtorque.
The applicant should apply this value during the maximum overtorque test.
c. Test conditions. The required test conditions specified in § 33.84(b) apply to the declared maximum engine overtorque. The applicant should incorporate the test into the endurance sequence for the rated power where the overtorque occurs. For example, when the maximum overtorque is associated with the 30-minute OEI rating, the 15 minute test time required in § 33.84(b)(1) may be incorporated into § 33.87(c)(4), either by running the entire 15 minutes during one of the 25 endurance cycles, or splitting the 15 minutes among the 25 endurance cycles into periods of not less than 2½ minutes each. The following test parameters apply:
(1) The power turbine rotational speed must be equal to the highest speed at which the maximum overtorque can occur in service. It should not exceed the limit speed associated with the rating for which the maximum overtorque is considered.
(2) The turbine-entry gas temperature must be equal to the maximum steady-state temperature approved for use during periods longer than 20 seconds when operating at conditions not associated with 30-second or 2-minute OEI ratings. We may waive the requirement to run the test at the maximum approved steady-state temperature if the applicant shows that other testing provides the desired temperature effects when considered in combination with the other parameters identified in §§ 33.84(b)(1), (b)(2), and (b)(3).
(3) The engine oil temperature should be within the normal operating range. For engines incorporating a reduction gearbox, the gearbox oil temperature must be equal to the maximum temperature when the maximum engine overtorque could occur in service.
d Post-test engine inspection. The engine subjected to the maximum overtorque during the endurance test under § 33.87 must meet the teardown inspection requirements, §§ 33.93(a)(1) and (a)(2), which we discuss further in chapter 4 of this AC.