Rules on engine certification...

From:         rdd@netcom.com (Robert Dorsett)
Date:         04 Aug 96 16:44:51 
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... relating to blade separation (from FAR 25 and FAR 33).  As a bonus,
I included the "bird" section. :-)

The complete text of these sections is on:
	ftp://ftp.faa.gov/pub/files/avr/afs/fars/


===================================================

Sec. 25.571  Damage--tolerance and fatigue evaluation of structure.

  (a) General. An evaluation of the strength, detail design, and fabrication
must show that catastrophic failure due to fatigue, corrosion, or accidental
damage, will be avoided throughout the operational life of the airplane. This
evaluation must be conducted in accordance with the provisions of paragraphs
(b) and (e) of this section, except as specified in paragraph (c) of this
section, for each part of the structure which could contribute to a
catastrophic failure (such as wing, empennage, control surfaces and their
systems, the fuselage, engine mounting, landing gear, and their related
primary attachments). Advisory Circular AC No. 25.571-1 contains guidance
information relating to the requirements of this section (copies of the
advisory circular may be obtained from the U.S. Department of Transportation,
Publications Section M443.1, Washington, D.C. 20590). For turbojet powered
airplanes, those parts which could contribute to a catastrophic failure must
also be evaluated under paragraph (d) of this section. In addition, the
following apply:
  (1) Each evaluation required by this section must include--
  (i) The typical loading spectra, temperatures, and humidities expected in
service;
  (ii) The identification of principal structural elements and detail design
points, the failure of which could cause catastrophic failure of the
airplane; and
  (iii) An analysis, supported by test evidence, of the principal structural
elements and detail design points identified in paragraph (a)(1)(ii) of this
section.
  (2) The service history of airplanes of similar structural design, taking
due account of differences in operating conditions and procedures, may be
used in the evaluations required by this section.
  (3) Based on the evaluations required by this section, inspections or other
procedures must be established as necessary to prevent catastrophic failure,
and must be included in the Airworthiness Limitations section of the
Instruction for Continued Airworthiness required by Sec. 25.1529.
  (b) Damage-tolerance evaluation. The evaluation must include a
determination of the probable locations and modes of damage due to fatigue,
corrosion, or accidental damage. The determination must be by analysis
supported by test evidence and (if available) service experience. Damage at
multiple sites due to prior fatigue exposure must be included where the
design is such that this type of damage can be expected to occur. The
evaluation must incorporate repeated load and static analyses supported by
test evidence. The extent of damage for residual strength evaluation at any
time within the operational life must be consistent with the initial
detectability and subsequent growth under repeated loads. The residual
strength evaluation must show that the remaining structure is able to
withstand loads (considered as static ultimate loads) corresponding to the
following conditions:
  (1) The limit symmetrical maneuvering conditions specified in Sec. 25.337
at VC and in Sec. 25.345.
  (2) The limit gust condition specified in Secs. 25.305(d), 25.341, and
25.351(b) at the specified speeds up to Vc, and in Sec. 25.345.
  (3) The limit rolling conditions specified in Sec. 25.349 and the limit
unsymmetrical conditions specified in Secs. 25.367 and 25.427, at speeds up
to VC.
  (4) The limit yaw maneuvering conditions specified in Sec. 25.351(a) at the
specified speeds up to VC.
  (5) For pressurized cabins, the following conditions:
  (i) The normal operating differential pressure combined with the expected
external aerodynamic pressures applied simultaneously with the flight loading
conditions specified in paragraphs (b) (1) through (4) of this section, if
they have a significant effect.
  (ii) The expected external aerodynamic pressures in 1 g flight combined
with a cabin differential pressure equal to 1.1 times the normal operating
differential pressure without any other load.
  (6) For landing gear and directly-affected airframe structure, the limit
ground loading conditions specified in Secs. 25.473, 25.491, and 25.493.

If significant changes in structural stiffness or geometry, or both, follow
from a structural failure, or partial failure, the effect on damage tolerance
must be further investigated.
  (c) Fatigue (safe-life) evaluation. Compliance with the damage-tolerance
requirements of paragraph (b) of this section is not required if the
applicant establishes that their application for particular structure is
impractical. This structure must be shown by analysis, supported by test
evidence, to be able to withstand the repeated loads of variable magnitude
expected during its service life without detectable cracks. Appropriate safe-
life scatter factors must be applied.
  (d) Sonic fatigue strength. It must be shown by analysis, supported by test
evidence, or by the service history of airplanes of similar structural design
and sonic excitation environment, that--
  (1) Sonic fatigue cracks are not probable in any part of the flight
structure subject to sonic excitation; or
  (2) Catastrophic failure caused by sonic cracks is not probable assuming
that the loads prescribed in paragraph (b) of this section are applied to all
areas affected by those cracks.
  (e) Damage-tolerance (discrete source) evaluation. The airplane must be
capable of successfully completing a flight during which likely structural
damage occurs as a result of--
  (1) Impact with a 4-pound bird at Vc at sea level to 8,000 feet;
  (2) Uncontained fan blade impact;
  (3) Uncontained engine failure; or
  (4) Uncontained high energy rotating machinery failure.

The damaged structure must be able to withstand the static loads (considered
as ultimate loads) which are reasonably expected to occur on the flight.
Dynamic effects on these static loads need not be considered. Corrective
action to be taken by the pilot following the incident, such as limiting
maneuvers, avoiding turbulence, and reducing speed, must be considered. If
significant changes in structural stiffness or geometry, or both, follow from
a structural failure or partial failure, the effect on damage tolerance must
be further investigated.

[Amdt. 25-45, 43 FR 46242, Oct. 5, 1978, as amended by Amdt. 25-54, 45 FR
60173, Sept. 11, 1980; Amdt. 25-72, 55 FR 29776, July 20, 1990]

*****************************************************************************



Sec. 25.1461  Equipment containing high energy rotors.

  (a) Equipment containing high energy rotors must meet paragraph (b), (c),
or (d) of this section.
  (b) High energy rotors contained in equipment must be able to withstand
damage caused by malfunctions, vibration, abnormal speeds, and abnormal
temperatures. In addition--
  (1) Auxiliary rotor cases must be able to contain damage caused by the
failure of high energy rotor blades; and
  (2) Equipment control devices, systems, and instrumentation must reasonably
ensure that no operating limitations affecting the integrity of high energy
rotors will be exceeded in service.
  (c) It must be shown by test that equipment containing high energy rotors
can contain any failure of a high energy rotor that occurs at the highest
speed obtainable with the normal speed control devices inoperative.
  (d) Equipment containing high energy rotors must be located where rotor
failure will neither endanger the occupants nor adversely affect continued
safe flight.

[Amdt. 25-41, 42 FR 36971, July 18, 1977]




Sec. 33.19  Durability.

  (a) 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. Energy levels and trajectories of fragments
resulting from rotor blade failure that lie outside the compressor and
turbine rotor cases must be defined.
  (b) Each component of the propeller blade pitch control system which is a
part of the engine type design must meet the requirements of Sec. 35.42 of
this chapter.

Sec. 33.75  Safety analysis.

  It must be shown by analysis that any probable malfunction or any probable
single or multiple failure, or any probable improper operation of the engine
will not cause the engine to--
  (a) Catch fire;
  (b) Burst (release hazardous fragments through the engine case);
  (c) Generate loads greater than those ultimate loads specified in Sec.
33.23(a); or
  (d) Lose the capability of being shut down.

[Amdt. 33-6, 39 FR 35467, Oct. 1, 1974, as amended by Amdt. 33-10, 49 FR
6852, Feb. 23, 1984]

Sec. 33.77  Foreign object ingestion.

  (a) Ingestion of a 4-pound bird, under the conditions prescribed in
paragraph (e) of this section, may not cause the engine to--
  (1) Catch fire;
  (2) Burst (release hazardous fragments through the engine case);
  (3) Generate loads greater than those ultimate loads specified in Sec.
33.23(a); or
  (4) Lose the capability of being shut down.
  (b) Ingestion of 3-ounce birds or 1 1/2 -pound birds, under the conditions
prescribed in paragraph (e) of this section, may not--
  (1) Cause more than a sustained 25 percent power or thrust loss;
  (2) Require the engine to be shut down within 5 minutes from the time of
ingestion; or
  (3) Result in a potentially hazardous condition.
  (c) Ingestion of water, ice, or hail, under the conditions prescribed in
paragraph (e) of this section, may not cause a sustained power or thrust loss
or require the engine to be shut down. It must be demonstrated that the
engine can accelerate and decelerate safely while inducting a mixture of at
least 4 percent water by weight of engine airflow following stabilized
operation at both flight idle and takeoff power settings with at least a 4
percent water-to-air ratio.
  (d) For an engine that incorporates a protection device, compliance with
this section need not be demonstrated with respect to foreign objects to be
ingested under the conditions prescribed in paragraph (e) of this section if
it is shown that--
  (1) Such foreign objects are of a size that will not pass through the
protective device;
  (2) The protective device will withstand the impact of the foreign objects;
and
  (3) The foreign object, or objects, stopped by the protective device will
not obstruct the flow of induction air into the engine with a resultant
sustained reduction in power or thrust greater than those values required by
paragraphs (b) and (c) of this section.
  (e) Compliance with paragraphs (a), (b), and (c) of this section must be
shown by engine test under the following ingestion conditions:

   Foreign                        Speed of          Engine
   object      Test quantity   foreign object     operation       Ingestion

Birds:
 3-ounce size  One for each    Liftoff speed    Takeoff         In rapid
                50 square       of typical                       sequence to
                inches of       aircraft                         simulate a
                inlet area or                                    flock
                fraction                                         encounter
                thereof up to                                    and aimed at
                a maximum of                                     selected
                16 birds.                                        critical
                Three-ounce                                      areas.
                bird
                ingestion not
                required if a
                1 1/2 -pound
                bird will
                pass the
                inlet guide
                vanes into
                the rotor
                blades
 1 1/2 -pound  One for the     Initial climb    Takeoff         In rapid
  size          first 300       speed of                         sequence to
                square inches   typical                          simulate a
                of inlet        aircraft                         flock
                area, if it                                      encounter
                can enter the                                    and aimed at
                inlet, plus                                      selected
                one for each                                     critical
                additional                                       areas.
                600 square
                inches of
                inlet area or
                fraction
                thereof up to
                a maximum of
                8 birds
 4-pound size  One, if it can  Maximum climb    Maximum cruise  Aimed at
                enter the       speed of                         critical
                inlet           typical                          area.
                                aircraft if
                                the engine has
                                inlet guide
                                vanes
                               Liftoff speed    Takeoff         Aimed at
                                of typical                       critical
                                aircraft, if                     area.
                                the engine
                                does not have
                                inlet guide
                                vanes
Ice            Maximum         Sucked in        Maximum cruise  To simulate a
                accumulation                                     continuous
                on a typical                                     maximum
                inlet cowl                                       icing
                and engine                                       encounter at
                face                                             25 deg.F.
                resulting
                from a 2-
                minute delay
                in actuating
                anti-icing
                system, or a
                slab of ice
                which is
                comparable in
                weight or
                thickness for
                that size
                engine
Hail (0.8 to   For all         Rough air        Maximum cruise  In a volley
 0.9 specific   engines: With   flight speed     at 15,000       to simulate
 gravity)       inlet area of   of typical       feet altitude   a hailstone
                not more than   aircraft                         encounter.
                100 square                                       One-half the
                inches: one                                      number of
                1-inch                                           hailstones
                hailstone.                                       aimed at
                With inlet                                       random area
                area of more                                     over the
                than 100                                         face of the
                square                                           inlet and
                inches: one                                      the other
                1-inch and                                       half aimed
                one 2-inch                                       at the
                hailstone for                                    critical
                each 150                                         face area.
                square inches
                of inlet area
                or fraction
                thereof
               For supersonic  Supersonic       Maximum cruise  Aimed at
                engines (in     cruise                           critical
                addition): 3    velocity.                        engine face
                hailstones      Alternatively,                   area.
                each having a   use subsonic
                diameter        velocities
                equal to that   with larger
                in a straight   hailstones to
                line            give
                variation       equivalent
                from 1 inch     kinetic energy
                at 35,000
                feet to 1/4
                inch at
                60,000 feet
                using
                diameter
                corresponding
                to the lowest
                supersonic
                cruise
                altitude
                expected
Water          At least 4      Sucked in        Flight idle,    For 3 minutes
                percent of                       acceleration,   each at idle
                engine                           takeoff,        and takeoff,
                airflow by                       deceleration    and during
                weight                                           acceleration
                                                                 and
                                                                 deceleration
                                                                 in spray to
                                                                 simulate
                                                                 rain.

Note.--The term "inlet area" as used in this section means the engine inlet
projected area at the front face of the engine. It includes the projected
area of any spinner or bullet nose that is provided.

[Amdt. 33-10, 49 FR 6852, Feb. 23, 1984]

Sec. 33.92  Windmilling tests.

  (a) For engines to be used in supersonic aircraft, unless means are
incorporated in the engine to stop rotation of the engine rotors when the
engine is shut down in flight, each engine rotor must either seize or be
capable of rotation for 3 hours at the limiting windmilling rotational r.p.m.
with no oil in the engine system, without the engine--
  (1) Catching fire;
  (2) Bursting (releasing hazardous uncontained fragments); or
  (3) Generating loads greater than those ultimate loads specified in Sec.
33.23(a).
  (b) A turbojet or turbofan engine incorporating means to stop rotation of
the engine rotors when the engine is shut down in flight must be subjected to
25 operations under the following conditions:
  (1) Each engine must be shut down while operating at rated maximum
continuous thrust.
  (2) For engines certificated for use on supersonic aircraft, the
temperature of the induction air and the external surfaces of the engine must
be held at the maximum limit during the tests required by this paragraph.

Sec. 33.94   Blade containment and rotor unbalance tests.

  (a) Except as provided in paragraph (b) of this section, it must be
demonstrated by engine tests that the engine is capable of containing damage
without catching fire and without failure of its mounting attachments when
operated for at least 15 seconds, unless the resulting engine damage induces
a self shutdown, after each of the following events:
  (1) Failure of the most critical compressor or fan blade while operating at
maximum permissible r.p.m. The blade failure must occur at the outermost
retention groove or, for integrally-bladed rotor discs, at least 80 percent
of the blade must fail.
  (2) Failure of the most critical turbine blade while operating at maximum
permissible r.p.m. The blade failure must occur at the outermost retention
groove or, for integrally-bladed rotor discs, at least 80 percent of the
blade must fail. The most critical turbine blade must be determined by
considering turbine blade weight and the strength of the adjacent turbine
case at case temperatures and pressures associated with operation at maximum
permissible r.p.m.
  (b) Analysis based on rig testing, component testing, or service experience
may be substitute for one of the engine tests prescribed in paragraphs (a)(1)
and (a)(2) of this section if--
  (1) That test, of the two prescribed, produces the least rotor unbalance;
and
  (2) The analysis is shown to be equivalent to the test.