SECTION 12, MAIN COMPONENT REQUIREMENTS * 205. § 29.547 (through Amendment 29-19) MAIN ROTOR STRUCTURE.
a. Explanation. This regulation requires the main rotor structure to be designed to the static load requirements of $$ 29.337 through 29.351 (vertical maneuvering loads, vertical and horizontal gust loads, and yawing maneuver loads). In addition, the main rotor blades, hubs, and flapping hinges are specified to be designed for impact forces of each blade against its stop during ground operation and for specified limit torque at any rotational speed including zero. The torque forces (from the drive system) are distributed to the rotor blades as specified.
b. Procedures.
(1) Substantiation in compliance with this standard is accomplished by application of the flight loads of §§ 29.337 through 29.351 and the torque loads of § 29.361 to the rotor structure by stress analyses and/or static tests. The use of wind tunnel data as well as flight loads survey data may be used to generate and/or check the external load magnitudes and distributions.
(2) Where new materials are used in the main rotor structure, such as composites containing plastics, the effects of temperature and humidity are to be considered in accordance with § 29.603, and the effects of uncertainties in manufacturing processes or inspection methods are to be considered in accordance with § 29.619.
(3) The design impact forces of each blade must be imposed against its stop or stops. Appropriate monitoring of the blades, hubs, flapping hinges, and stops during laboratory tests, ground endurance tests, and flight tests should ensure that the stops are sufficient for ground operation loads. The design torque loads are derived as prescribed.
206. § 29.549 (through Amendment 29-19) FUSELAGE AND ROTOR PYLON.
a • Explanation. This regulation requires that the fuselage and rotor pylon (including the tail fin, if any) be designed to withstand the flight loads of §§ 29.337 through 29.351, the ground loads of §§ 29.235, 29.471 through 29.497, sk1 loads of § 29.505, water loads of § 29.521, and rotor loads of § 29.547(d) (1) and (e) (1) (1). The ski and water loads pertain to optional features.
(1) Consideration is also required of--
(1) Auxiliary rotor thrust;
(ii) The torque reaction of each rotor drive system; and
(111) Balancing air and inertia loads.
• Chap 2 Par 205 315
AC 29-2, CHG 1 11/19/84 * (2) Each engine mount and adjacent fuselage must be substantiated as prescribed. In addition, if 2 1/2-minute power is used, "each engine mount and adjacent structure must be designed to withstand the loads resulting from a limit torque equal to 1.25 times the mean torque for 2 1/2-minute power combined with "g flight loads."
b. Procedures. Compliance with this standard is accomplished by application of the specified aircraft loads including engine torque to the fuselage and rotor pylon struoture by stress analyses and/or static tests. Drive system torque factors to be used are noted in $ 29.547 for the main rotor structure as well as in paragraph (e) of this standard.
207. § 29.551 (through Amendment 29-19) AUXILIARY LIFTING SURFACES.
a. Explanation. This regulation specifies that auxiliary lifting surfaces be designed to withstand critical flight and ground loads derived for conditions specified and any "other critical condition expected in normal operation." Stub wings would comply with this standard.
b. Procedures. The surface design loads are derived from the conditions specified. Conservative aerodynamic data, including load distributions, may be used in place of data derived from wind tunnel or instrumented flight testing of the exact aerodynamic shapes involved. Special attention should be placed on concentrated load effects from fuel tanks or other large mass items that may be located in lifting surfaces. These types of load concentrations are to be
208.-217. RESERVED.
SECTION 13. EMERGENCY LANDING CONDITIONS
218. § 29.561 GENERAL (RESERVED)
219. § 29.563 (through Amendment 29-19) STRUCTURAL DITCHING PROVISION.
a • Explanation. Amendment 29-12 included certification requirements for ditching approvals. The helicopters must be able to sustain an emergency landing in water as prescribed by § 29.801(e).
b• Procedures. Refer to paragraph 337, § 29.801, for procedures,
220.-229. RESERVED.
Chap 2 316 (thru 372) Par 206
* 251. § 29.625 (through Amendment 29-19) FITTING FACTORS.
a. Explanation. A 1.15 factor 18 specified to assure that the calculated load and stress distribution within any fitting is conservative. Application of the factor is excluded or excepted as stated in the rule.
b. Procedures.
(1) The factor may be applied to the calculated load or stress for the fitting.
(2) The structural substantiating data for the rotorcraft, including the rotor system, must include the prescribed fitting factor. The rotor system includes the flight control system rotor head and hubs and rotor blade attachments.
252. § 29.629 (through Amendment 29-19) FLUTTER.
a • Explanation•
(1) The rotororaft must be free from flutter.
(2) Section 29.251 vibration is an associated flight requirement concerning flight demonstrations. See paragraph 110 of this document for this standard.
(3) Section 29.571(a)(3) concerns in-flight measurement of loads or stresses.
b. Procedures.
(1) Freedom from flutter may be shown by analysis or appropriately instrumented flight flutter tests.
(2) The flight loads survey proposal submitted for compliance with § 29.571 may also contain tests to fulfill compliance with § 29.629. The flight loads survey program encompasses the envelope of design airspeed and rotor
r.p.m., and sufficient aerodynamic excitation is generally present to excite any latent flutter modes.
(3) Flight loads survey data or flight flutter test data submitted should be reviewed to assure that excessive oscillatory loads of rotors or surfaces will not be encountered.
253.-264. RESERVED.
Chap 2 Par 251 411 (thru 429)
AC 29-2, CHG 1 11/19/84 SECTION 16 ROTORS
265. § 29.653 PRESSURE VENTING AND DRAINING OF ROTOR BLADES. (RESERVED)
266. $ 29.659 MASS BALANCE. (RESERVED) * 267. § 29.661 (through Amendment 29-19) ROTOR BLADE CLEARANCE.
a • Explanation.
(1) The rotors, main and tail, must not strike other parts of the rotorcraft during any operating condition.
(2) Section 29.411 concerns protection of the tail rotor from a ground strike.
b. Procedures.
(1) The applicant should have drawings or sketches of the rotorcraft that show an adequate minimum clearance between the rotors, main and tail, and parts of the rotororaft. Probable flexing of the rotors should be considered in determining the minimum clearance.
(2) During parts of the FAA-conducted flight test program, frangible devices (wood dowels) or other means of measuring clearance, may be requested to confirm that the clearance shown in the drawings or sketches is adequate in certain operating conditions. Balsa wood dowels may be clamped to the aft part of the fuselage within the rotor arc. If the devices are intact after autorotation landing tests and other tests involving typical abrupt, cyclic, and rudder pedal displacements, the clearance should be satisfactory and compliance obtained. If such measuring devices are used, the type inspection report should contain a record of clearance found during the tests. It is not necessary to precisely determine the clearance but only necessary to determine enough clearance" as stated in the rule.
268. § 29.663 (through Amendment 29-19) GROUND RESONANCE PREVENTION MEANS.
a. Explanation,
(1) This rule, adopted in Amendment 29-3, requires reliability and damping action investigation for the ground resonance prevention means and requires associated maintenance information in the maintenance manual (§
29.1529). The probable range of variations in service, not just the allowable range, must be investigated as prescribed. This probable range includes operation on the ground, water, or other appropriate landing surface applicable to the rotorcraft design. Quantitative test data are generally obtained in compliance with this rule. See the preamble to Amendment 29-3 for further information.
(2) Note that the maintenance information is not contained in the approved section of the maintenance manual.
Chap 2 430 Par 265
during certain applicant and TIA verification evaluations or tests of the rotorcraft. Section 29.241 complements the requirements of § 29.663. As noted in paragraph 99 of this document, the FAA removed from CFR Part 7 a specific requirement for a ground vibration survey. However, § 29.663 was adopted by Amendment 29-3 to investigate possible sources of ground resonance and to assure the reliability of the ground resonance prevention means; 1.e., dampers to preclude occurrance of ground resonance. The total rotorcraft system is evaluated under this rule.
(4) Viscous dampers have been used for many years to prevent ground resonance. Modern rotorcraft designs may also use elastomeric dampers and may use elastomeric bearings in the rotor head and rotor pylon attachment to the airframe. The rule also requires investigation of the probable range of variations of these dampers and bearings to preclude ground resonance.
(5) Ground resonance can occur due to flexibility in the rotor pylon restraint system as well as with landing gear flexibilities. This evaluation Deutsch, JAS, Vol. 13, No. 5, May 1946).
b. Procedures.
The reliability of the means for preventing ground resonance may be substantiated as stated in the rule. An analysis report or a test proposal and subsequent test report may be used to show compliance. The probable ranges of damping restriction are an important part of the assessment. The test may be conduoted in conjunction with the testing required by § 29.241. See paragraph 99.
(1) Analysis and tests may be used;
(11) Reliable service history of identical or closely similar systems may be used. The materials and fluids used, olearance or fits, seals, and physical installation are important items to be evaluated and considered for "closely similar" systems;
(111) Testing of the complete rotorcraft may be used to prove that malfunction of a single means of the damping system will not cause ground resonance. One method of demonstrating acceptable compliance is by removing all seals from one damper, in conjunction with considering the allowable ranges of damping of the other parts of the rotorcraft damping system and operating the rotorcraft throughout the rotor speed range from start to maximun rotor speed.
The rotorcraft cyclic control should be displaced as noted in paragraph 99 of this document to assure that the possible rotororaft resonance frequencies are satisfactory. Each critioal rotor damper and landing gear damper must simulate malfunction to oomply with the rule. The testing discussed, however, could excited. If vibrations are damped in all tests, the damping system is Chap 2 Par 268 431
AC 29-2, CHG 1 11/19/84 * become very extensive if one were to attempt to test all combinations of all maintenance adjustments of all components which contribute to the prevention of ground resonance, while at the same time rendering each of the pertinent components ineffective in turn and then repeating all of the maintenance tolerance testing each time. Fortunately, rational analytical methods are available which will permit the evaluation of such combinations so that only the combinations with the least amount of margin used are physically tested.
(2) The probable ranges of damping must be investigated as prescribed and noted in subparagraph a(l). An approved test proposal and test results report should be used for complying with § 29.663(b). If wheel landing gear is used on the rotorcraft, the probable ranges of tire pressure or the lowest probable tire pressure should be stated in the test proposal and effects of the tire pressure investigated during the test. See paragraph 99, § 29.241, concerning tests and instrumentation of the test associated with complying with § 29.241. The instrumentation noted in paragraph 99 also applies to § 29.663(b).
(3) If the wheel landing gear is equipped with wheel brakes, the evaluation should include brakes "on" and "off." The nose or tail wheel should be looked and unlocked if it swivels to evaluate any possible adverse effects of this feature.
269.-278. RESERVED.
SECTION 17. CONTROL SYSTEMS
279. $ 29.671 GENERAL. (RESERVED)
280. $ 29.675 STOPS. (RESERVED)
281. $ 29.679 CONTROL SYSTEM LOCKS. (RESERVED)
282. $ 29.681 LIMIT LOAD STATIC TESTS. (RESERVED) 283- $ 29.683 OPERATION TESTS. (RESERVED)
284. $ 29.685 CONTROL SYSTEM DETAILS. (RESERVED)
285. $ 29.687 SPRING DEVICES. (RESERVED) 432 (thru 470) Chap 2 Par 268
(3) The required "down-lock" should be checked during the operation test. The design drawing should be reviewed for compliance prior to conducting an operation test.
(4) If an optional "up-lock" is installed, the landing gear should be extended during the operation test after simulation of critical failure mode of the retraction system.
§ 29.729(d) should include the items noted in the two previous subparagraphs and should include a functional check of the position indicator system. Those tests must be satisfactorily completed before issuing the TIA.
(6) During the official FAA flight tests, compliance with the emergency operation, position indicator, and control aspect of § 29.729(c), (e), and (f), respectively, will be verified or accomplished. In addition, the F and R test program plan (§ 21.35) will specify certain tests or evaluations for the retraction system.
(7) Position Indicator Evaluation.
(1) When evaluating the position indicator system, emphasis should be placed on the switches and their installations, and on the cockpit presentation. fach gear must have its own set of switches to indicate when it is secured in its extreme "up" position and its extreme "down" position. The switches must be located to give a valid indication of the arrival of the gear at its extreme position.
switches to be used should be carefully considered. An example of a condition that has potential for trouble is operation on wet areas. Trouble starts when water is picked up by the tires and deposited on the switches. During winter " the resting 0 may pr months the water can freeze, and the resulting ice may prevent the switch from functioning properly.
each gear. One light is colored "green" and indicates when its gear is secured in the extreme "down" position. The other light is colored "amber" and indicates when its gear is in transit. when the gear is in either extreme position, the in transit light is "out." For this presentation the indication to the pilot that the gear is in the extreme "up" position is an all-gear lights-out condition.
(iv) Some manufacturers have also included a warning system to alert the crew if the landing gear has not been extended prior to landing. If a warning system is presented, §§ 29.1301 and 29.1309 should be used to evaluate its functional characteristics and the impact of its failure modes.
Chap 2 Par 301 491
AC 29-2, CHG 1 11/19/84
302. 2 29.731 WHEELS. (RESERVED)
303. § 29.733 TIRES. (RESERVED)
304. § 29.735 BRAKES. (RESERVED)
305. 29.737 SKIS. (RESERVED)
306.-315. RESERVED.
SECTION 19. FLOATS AND HULLS
316. § 29.751 MAIN FLOAT BUOYANCY. (RESERVED)
317. $ 29.753 MAIN FLOAT DESIGN. (RESERVED)
318. § 29.755 HULL BUOYANCY. (RESERVED)
319. § 29.757 HULL AND AUXILIARY FLOAT STRENGTH. (RESERVED)
320.-329. RESERVED.
492 (thru 530) Chap 2 Par 302
SECTION 20. PERSONNEL AND CARGO ACCOMMODATIONS
330. § 29.771 PILOT COMPARTMENT. (RESERVED)
331. 229.773 PILOT COMPARTMENT VIEW. (RESERVED)
332. § 29.775 (through Amendment 29-19) WINDSHIELD AND WINDOWS.
a. Explanation. Nonsplintering safety glass 18 required in windshields and windows containing glass to protect crew and passengers in the event that window fracturing occurs.
b. Procedures. Use nonsplintering safety glass in windshield or window applications which contain glass rather than plastic acrylics, polycarbonates, epoxys, etc. The glass selected must meet a specification such as MIL-G-25871, and if new vendors are selected by an airframe manufacturer, test data should be obtained from the vendor to demonstrate the safety glass provided meets an acceptable specification and provides adequate nonsplintering capability.
333. 29.777 COCKPIT CONTROLS. (RESERVED)
334. § 29.783 (through Amendment 29-20) DOORS.
a - Explanation. This regulation requires at least one door for all closed cabin rotororaft. Standards for all doors and airstair doors are included. To assure that the doors provide normal entry and egress without causing or contributing to hazardous conditions, even after a minor crash, the following requirements are imposed:
(1) Passenger doors may not be located with respect to any rotor to endanger persons using the doors as instructed.
(2) Means are required for locking crew and external passenger doors to prevent their opening in flight due--
(1) To inadvertent operation; or
(11) To mechanical failure.
(3) External doors are required to be openable from the inside or outside by simple and obvious means.
(4) Reasonable provisions to prevent Jamming of external doors are required as specified and to assure that an "airstair door" is useable.
locked are required: (5) The following visual indications of external doors being olosed and, Chap 2 Par 330 531 (thru 547)
AC 29-2, CHG 1 11/19/84 * Direct visual inspection means by crewmembers of the locking mechanism of all external doors.
(11) Visual means to signal to crewmembers "when normally used external doors are closed and fully locked.
(6) For certain outward opening doors, an auxiliary safety latching device is required &to prevent the door from opening when the primary latching mechanism fails. Suitable operating procedures to prevent this device from being used during takeoff and landing are required if the door cannot be opened from outside the rotorcraft (ref. § 29.783(c)) with the device in place.
b. Procedures•
(1) Passenger doors should be located as far as possible from the auxiliary rotorg. The doors may be hinged and door open stops may be provided to separate entering and egressing passengers from the auxiliary rotor blades. If necessary for the design, "appropriate instructions" should be provided for all passenger doors concerning entering and leaving the rotorcraft and safe use of each door relative to all rotors. These instructions should be obvious to a passenger using the door, contain large enough letters to be readily legible, and use letters or background colors associated with danger (1.e. orange or red).
(2) Means to prevent the opening of doors in flight.
inadvertent operation may be provided by recessing door handles to prevent their inadvertent operation by the normal movement of passengers about the cabin. If recessing the door handle is impractical, a cover may be provided which will prevent inadvertent operation of the handle, but the cover should be of such design that it does not obscure the door handle nor its operating instructions.
It must not unduly interfere with deliberate operation of the door handle by passenger or crew. Transparent or nonsolid covers, easily displaced by deliberate actions, have been used to prevent inadvertent door handle operation. Some rotorcraft designs meet this requirement by requiring that passengers wear their seat belts at all times during flight. This design requires that the 'fasten seat belt sign be on at all times the rotorcraft is in flight (for practical purposes, the "fasten seat belt" light is generally designed to be on when power is applied to the rotorcraft).
(11) Means to prevent inadvertent door opening in flight due to "mechanical failure" is most efficiently provided by multiple door latches and multiple load path door locking mechanisms so that the door will remain locked after a single failure. Care should be taken in the design of multiple load path latohes and mechanisms to assure independence of all failures and to consider the effort of deflections after failures (if a failure allows deflections into the airstream sufficient to increase aerodynamic loads, the increase in loads should be accounted for; if a failure allows significant movement of latching components, the derlections should be accurately accounted for to assure that disengagement of nonfailed latches does not occur).
Chap 2 548 Par 334
(3) The means to open normally used external doors is required to be simple (such as a rotating handle) and to be accessible from the inside or the outside. To prevent the inadvertent use of emergency exits (separate from normal entry doors) for routine entry and exit with the resulting "wear and tear," the normally used doors for entry and exits should be equipped with operating handles and instructions distinctly different from those of the emergency exits.
Obviously, the above does not apply to normally used exits which are also the primary (or only) emergency exits.
(4) Reasonable provisions to prevent jamming of external doors include the following:
(1) Design features of doors which are insensitive to large fuselage deflections for door operation.
(i1) Provision of clearance between door and door frame latching devices sufficient to allow some relative deflection between the door and door frame and still allow door operation. The relative deflections may be determined by static test or by an analyais approved by the FAA.
Sliding doors are frequently used in transport helicopters for versatility and utility reasons. If sliding doors are used, one of the following features of design may be required to assure that the requirements of § 29.783(d) are met:
(A) The sliding door(s) must be provided with Jettison features which allow release of the door(s)from the tracks (to preclude Jamming).
The emergency release is generally separate and distinct from the normal door handle.
(B) Separate emergency exits of appropriate size and number may be installed in the sliding door(s).
(C) Separate emergency exits of appropriate gize and number may be installed in addition to the sliding door(s).
Whether or not the sliding door is qualified as an emergency exit, it must meet the remaining door design standards. mechanism of external doors may provide for visual observation of the door frame , of the looking frame and the latching components for engagement or for visual observation of "flag" areas of the locking mechanism. If "flag" areas are used (such as tabs or shoulders which protrude into the crewmember's line of sight when the latches are engaged (locked)), care should be taken to assure that the tab is permanently affixed (or an integral part) to the looking mechanism; and it should not give of the latching mechanism. "Visual means to signal" to crewmembers "when normally, erroneous readings to the crewmembers under any foreseeable operation or failure used external doors are closed and fully locked" may be provided by annunciator Chap 2 Par 334 549
AC 29-2, CHG 1 11/19/84 * panel lights or equivalent means. The visual indicating system may consist of an indicator for each individual door, or a system connecting all doors in series.
If the latter system is used, it need not necessarily show which door is not fully locked. It is not necessary that more than one crewmember be able to ascertain by a visual signal that all external doors normally used by the crew in supplying the rotorcraft, or in loading and unloading passengers and cargo, are fully closed and The visual signal should be located so that it may easily be seen by the appropriate crewmember from his station.
(6) For § 29.783(f), the auxiliary safety latching device to "prevent the door from opening when the primary latching mechanism fails" can be provided by the same multiple load path features which neet the § 29.783(c) requirement for prevention of door opening in flight after a "mechanical failure." If a completely separate "auxiliary safety latching device" is used, it should allow the door to be opened from the inside, or outside, when in place. If the device must be removed to allow use of the door, "suitable operating procedures" (1.e., placards and RFM instructions) will be required for removal of the device during
(7) Additional standards for "airstair doors" were added by Amendment 29-20.
An analysis or test may be used to prove compliance with deformation standards in § 29.783(g) (1).
A sketch, drawing, or demonstration may be used to prove the door is useable for the conditions described in § 29.783(g) (2).
335. § 29.785 (through Amendment 29-19) SEATS, SAFETY BELTS, AND HARNESSES.
a • Explanation
(1) This section requires that seats, belts, harnesses, and adjacent parts of the rotorcraft be substantiated for the structural loads resulting from the inertia forces of § 29.56l as well as normal flight and ground inertia forces on a 170-pound occupant. The inertia forces of § 29.561 are ultimate loads and must be multiplied by a factor of 1.33 in determining the "strength of attachment" of each seat to structure and each belt or harness to structure. The seat, belt, etc., are required to sustain applied loads and to protect the occupant from serious injury. The pilot seats must also sustain the effects of the pilot forces of $ 29.397.
(2) In addition, the "occupant must be protected from head injury" by the seat belt and one of the following:
(1) A harness to prevent the head from contacting an injurious • object.
Chap 2 550 Par 334