Appendix 1

Extract 1

Extract from Federal Airworthiness Regulations FAR 25 Engines

GENERAL

§25.901 Installation

(a) For the purpose of this part, the airplane powerplant installation includes each component that -

(1) Is necessary for propulsion;

(2) Affects the control of the major propulsive units; or

(3) Affects the safety of the major propulsive units between normal inspections or overhauls.

(b) For each powerplant -

(1) The engine installation must meet the applicable provisions of this subpart;

(2) The components of the installation must be constructed, arranged, and installed so as to ensure their continued safe operation between normal inspections and overhauls.

§25.903 Engines

(a) Engine type certification. Each engine must be type certificated under Part 33.

§25.939 Turbine engine operating characteristics

(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause vibration harmful to the engine.

Extract from Federal Airworthiness Regulations FAR 33 ENGINES

§33.11 Applicability

This subpart prescribes the general design and construction requirements for reciprocating and turbine aircraft engines.

§33.19 Durability

Engine design and construction must minimize the development of an unsafe condition of the engine between overhaul periods. The design of the compressor and turbine rotor cases must provide for the containment of damage from rotor blade failure.

3.3.2 The blade rows to be investigated and the number of blades in each row shall be agreed with the Authority. The blade rows will normally include:

(a) the first compressor rotor blade row, all rows adjacent to variable incidence stator blades, and these stator blades if cantilevered, ie unshrouded,

(b) the last turbine blade row and the adjacent stator turbine blades if cantilevered,

(c) as many other rows of compressor and turbine rotor blades and the adjacent stator blades if they are cantilevered, as may be shown from the best results of (a) and (b) to be necessary.

NOTE: Should the investigation indicate resonances of large amplification factor in the above rows of blading, or should the investigation, development experience, calculation, etc, suggest that such resonances may be expected to occur in other rows of blading, the Authority reserves the right to require the vibration survey to be extended as necessary. In estimating from limited measurements the highest stresses likely to be experienced in the worst blade of any row, allowance should be made for the inevitable scatter in peak amplitudes which will occur when blades have the usual production tolerances on frequency.

3.4 Engine Carcass. Acceptable levels of Engine carcass vibrations shall be established from experience of development and type testing, and shall be declared for selected datum positions.

NOTE: These will be used in assessing the vibration characteristics of the Engine when installed in an aeroplane.

Extract from Joint Airworthiness Requirements JAR 25 LARGE AEROPLANES

JAR 25.939 Turbine engine operating characteristics

(a) Turbine engine operating characteristics must be investigated in flight to determine that no adverse characteristics (such as stall, surge, or flame-out) are present, to a hazardous degree, during normal and emergency operation within the range of operation limitations of the aeroplane and of the engine. (See ACJ 25.939(a).

(b) Reserved

(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause vibration harmful to the engine. (See ACJ 25.939(c).

(d) It must be established over the range of operating conditions for which certification is required that the powerplant installation does not induce engine carcass vibration in excess of the acceptable levels established during engine type certification under JAR-E, C3-4, paragraph 3.4. (See ACJ 25.939(d).

ACJ 25.939(a)

Turbine Engine Operating Characteristics (Interpretative Material)

See JAR 25.939(a)

1. The wording 'in flight' should be interpreted to coverall all operating conditions from engine start until shut-down.

2. If the airflow conditions at the engine air intake can be affected by the operating conditions of an adjacent engine, the investigation should include an exploration of the effects of running the adjacent engine at the same and at different conditions over the whole range of engine operating conditions, including reverse thrust. An investigation of the effect of malfunctioning of an adjacent engine should also be included.

ACJ 25.939(c)

Turbine Engine Operating Characteristics (Acceptable Means of Compliance and Interpretative Material

1. The investigation should cover the complete range, for which certification is required, of aeroplane speeds attitudes, altitudes and engine operating conditions including reverse thrust, and of steady and transient conditions on the ground and in flight, including crosswinds, rotation, yaw and stall. Non-critical conditions of operation which need not be considered should be agreed with the Authority.

2. If the airflow conditions at the engine air intake can be affected by the operating conditions of an adjacent engine, the investigation should include an exploration of the effects of running the adjacent engine at the same and at different conditions over the whole range of engine operating conditions, including reverse thrust. An investigation of the effect of malfunctioning of an adjacent engine should also be included.

3. Compliance with the requirement may include any suitable one or combination of the following methods; as agreed with the Authority.

a. Demonstration that the variations in engine inlet airflow distortion over the range defined in 1 are within the limits established for the particular engine type.

b. An investigation of blade vibration characteristics by the method and of the scope indicated in JAR-E, C3-4 para 3.3 (except that Maximum Take-off rpm need not be exceeded) carried out on:

i. a representative installation on the ground using test equipment where the actual conditions of operation in the aeroplane are reproduced, or

ii. a representative aeroplane on the ground and in flight as appropriate to the conditions being investigated.

c. The completion of sufficient flying with representative installations prior to certification such as to demonstrate that the vibration levels are satisfactory.

d. Any other method acceptable to the Authority.

ACJ 25.939(d)

Turbine Engine Operating Characteristics (Acceptable Means of Compliance)

See JAR 25.939(d)

Compliance with JAR 25.939(d)

Compliance with JAR 25.939(d) may consist of flight tests using vibration measuring equipment on which engine test bed vibration levels were established, or the equipment intended to be supplied on production engines provided the Authority considers the equipment sensitive enough for the purpose of showing compliance with the requirements.

Extract from Joint Airworthiness Requirements JAR E ENGINES

3 VIBRATION SURVEYS Vibration surveys shall be made on the major rotating parts, compressor and turbine blading, and the Engine carcass.

3.1 General

3.1.1 Each survey shall cover all Engine conditions from Ground Idling to at least Maximum Engine Overspeed. Should there be any indication of a stress peak arising at high speed conditions, the survey shall be extended sufficiently to reveal the maximum stress values present, except that the survey need not extend beyond 105% of the maximum speed to be approved (other than Maximum Engine Overspeed) or 2% above Maximum Engine Overspeed, whichever is the higher.

3.1.2 Each survey shall enable an evaluation to be made of the effects, if appropriate to the particular part of the Engine being surveyed, of running with the most adverse compressor intake airflow distortion pattern declared by the constructor and the most adverse exhaust conditions, including the use of a thrust reverser.

3.1.3 The effects of likely fault conditions (such as out-of-balance, turbine entry blockage, fuel nozzle blockage, etc.) shall also be evaluated, if appropriate to the particular part of the Engine being surveyed.

3.1.4 For turbo-propeller Engines a representative flight propeller shall be fitted in cases where the results could be influenced by the presence of the Propeller.

3.2 Compressor and Turbine Rotors. It shall be shown by tests on an Engine or by other acceptable means that no dangerous vibratory stresses are likely to occur in compressor and turbine rotors (ie discs or drums) within the range of rpm covered by the survey.

NOTE: The evaluation of shafts is detailed in C3-4 App. 12.

3.3 Compressor and Turbine Blades

3.3.1 It shall be shown by strain gauging or other acceptable means that no unacceptable vibratory stresses are likely to occur in the compressor and turbine blading.

NOTES:

(1) If, to avoid unacceptable blade vibratory stresses, the constructor declares prohibited speed ranges, these should be agreed by the Authority.

(2) The blade vibration survey and the variation of the incremental running referred to in 6.6.1 may be waived wholly or in part if the Authority is satisfied that the total hours run on the test bed or in flight, under representative conditions, prior to certification, is such as to demonstrate that the vibration stress levels are satisfactory. This may apply particularly in the case of small Engines if the dimensions of the blades make it difficult to complete a satisfactory vibration survey.

§33.61 Applicability

This subpart prescribes additional design and construction requirements for turbine aircraft engines.

§33.61 Stress analysis

A stress analysis must be performed on each turbine engine showing the design safety margin of each turbine engine rotor, spacer, and rotor shaft.

§33.63 Vibration

Each engine must be designed and constructed to function throughout its normal operating range to rotational speeds and engine power without inducing excessive stress in any engine part because of vibration forces to the aircraft structure.

§33.82 General

Before each endurance test required by this subpart, the adjustment setting and functioning characteristic of each component having an adjustment setting and a functioning characteristic that can be established independent of installation on the engine must be established and recorded.

§33.83 Vibration test

(a) Each engine must undergo a vibration survey to establish the vibration characteristics of the rotors, rotor shafts, and rotor and stator blades at the maximum inlet air distortion limit, over the range of rotor shaft speeds and engine power or thrust, under steady state and transient conditions, from idling speed to 103 percent of the maximum desired takeoff speed rating. The survey must be conducted using, for turbopropeller engines, the same configuration of the propeller type which is used for the endurance test, and using, for other engines, the same configuration of the loading device type which is used for the endurance test.

(b) The vibration stresses of the rotors, rotor shafts, and rotor and stator blades may not exceed the endurance limit stress of the materials from which these parts are made. If the maximum stress in the shaft cannot be shown to be below the endurance limit by measurement, the vibration frequency and amplitude must be measured. The peak amplitude must be shown to produce a stress below the endurance limit; if not, the engine must be run at the condition producing the peak amplitude until, for steel part, 10 million stress reversals have been sustained without fatigue failure and, for other parts, until it is shown that fatigue failure will not occur within the endurance limit stress of the material.

(c) Each accessory drive and mounting attachment must be loaded, with the load imposed by each accessory used only for an aircraft service being the limit load specified by the applicant for the engine drive or attachment point.

Last modification on 1999-06-15 by Michael Blume