controls, and landing gear controls, it applies to all cockpit controls not addressed in other paragraphs.
b. Procedures.
(1) The cyclic should be mechanized such that movement of the control results in a corresponding sense of aircraft motion in the same axis. While a certain amount of coupling may be present following a pure control input in a given axis, that coupling should not be objectionable to the pilot. Collective pitch control should be mechanized such that an upward movement of the collective results in a corresponding relative motion of the aircraft in the vertical plane. Again, coupling should not be objectionable.
Care should be taken to insure that the primary pilot's perception of collective motion is in the vertical plane. The objective is to clearly differentiate collective motion from that associated with an airplane throttle. The rule is self-explanatory on the subject of engine power controls. A distinction is made between normal landing gear controls and emergency controls. Emergency controls may operate in a sense which might not correspond to the direction of resultant gear motion.
(2) The recommended operating convention and "switchology" for miscellaneous controls are:
Up/forward = on/increase (ії) Down/aft = off/decrease
(il) Variable rotary controls should move clockwise from the OFF position, through an increasing range, to the full ON position. For some variable intensity controls such as instrument lighting, the desired minimum setting may not be completely off. Pushbuttons not giving an obvious indication of mechanical position should be configured such that the flightcrew has a clear indication of switch actuation under both day and night (if applicable) conditions. Failure of the indication should be shown to be free of hazards.
(3) Slew or "beep" switches associated with flight control system applications warrant special attention. The recommended conventions for control-mounted single, or multifunction, two or four-way "beep" switches are:
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(i) Cyclic Flight Control System Switch Direction /Autopilot Configuration Aircraft Response forward/up basic trim nose down airspeed/groundspeed increased airspeed mode selected forward speed reference vertical speed mode increased rate of selected (without descent/decreased airspeed mode engaged) rate of climb hover mode selected increased groundspeed or forward acceleration reference left basic trim left wing down heading mode selected slow heading reference left hover mode selected increased groundspeed or acceleration reference to left (¡i) Collective (assumes switch is mounted on top of grip).
Flight Control System Switch Direction /Autopilot Configuration Aircraft Response forward control position hold down collective vertical speed mode increased rate of selected descent/decreased rate of climb hover mode selected decreased hover height reference left control position hold increase left pedal hover mode selected slow heading reference left Par 334 413
AC 27-1A 7130/97
(iii) Opinions are divided concerning the preferred convention for forward and rearward motion of slew switches mounted atop the collective grip. Part of the reason appears to stem from the fact that such a switch is never used in a purely control position trim capacity. The switch has normally remained nonfunctional until a vertical autopilot mode is selected. At that point, the switch is viewed by one pilot/engineer contingent as either an autopilot reference slew function or a power increase/decrease switch which should follow the "forward equals increase" convention.
The other group views the switch as a form of control position trim and finds the "forward equals down collective" convention to be more consistent with the sensing used for the cyclic beep switches. An obvious solution is to mount collective/vertical axis switches in a vertical orientation on the grip. Barring that alternative, viable arguments can be made for either philosophy. The recommended convention was selected following a survey of manufacturers and test pilots.
335. § 27.783 DOORS.
a. Explanation.
(1) Closed cabins must have at least one external door that is adequate and easily accessible for all of the occupants. The standard envisaged a door intended for normal use and for an emergency exit for all passengers. The passenger compartment, itself, should not be partitioned.
(2) Passenger doors should not be located near main or tail rotors such that persons using the door or doors would be endangered while entering or leaving the aircraft. The discs of engines or other propulsion system devices were not included in this standard. Procedures or instructions may be used to support compliance.
Section 27.1565 concerns tail rotor markings.
(3) Cabin doors of normal category rotorcraft should inherently comply with the exit standards in § 27.807(b) concerning the size of the unobstructed opening, accessibility, location, method of opening, arrangement, probable jamming due to fuselage deformation, and possibly markings inside and outside. The standards for the features and characteristics of exits should be applied to cabin doors unless an "exit" is also installed in the same side of the fuselage. The marking standards of § 27.1557(d) for exits should be applied to doors unless the door is readily identified and its opening features are simple and obvious. It is not necessary to use red and white colors, provided the door instructions and markings are conspicuous.
(4) If the door is used as a "ditching exit," the threshold of the door/exit must be above the waterline of the rotorcraft while in calm water (§ 27.807(d)). Note that "ditching approval" under § 27.801 is an optional standard.
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(5) If a lock is used as an optional feature, the lock must not engage inadvertently or, as a result of mechanical failure, prevent possible opening of the door from inside or outside the cabin.
b. Procedures.
(1) The layout of the most dense or critical (from evacuation aspect) interior arrangement should be reviewed as soon as possible in the certification program. Each passenger shall have easy access to each passenger door/exit. The crewmembers may have separate emergency exits or doors on each side of the aircraft separate from the passenger door if desired by the applicant. A mockup may be used to make an early assessment of the interior critical areas for door accessibility, operation of the door, door markings, and other features critical to compliance. A comprehensive interior compliance inspection may be accomplished later in the program to confirm or correct conclusions derived from a review of layout or mockup data.
(2) Mockup interiors used in the preliminary evaluation may not have all padding, liners, compartments; i.e., it may not be a fully equipped interior arrangement.
(3) The door should have clearance with the fuselage door frame to allow reasonable deflection without jamming, or the door may be designed to minimize jamming. So called "rip hinges" may be employed as well. Rip hinges may also serve as the primary emergency release for the door.
(4) If a door has an emergency release system for the door that is separate from a "normal open and close" system, certain standards of § 27.807(b) and (c) should apply.
(5) As good practice, internal and external markings are recommended for each door as tollows:
Indicate when the door is closed and fully locked.
(її) Indicate the means of opening.
(ili) Contrasting colors should be used in markings. Red and white are acceptable but not required. For exit markings, see § 27.1557(d).
(6) Crew and passengers should be protected from the main and tail rotors (discs) as prescribed in § 27.807(b). Two avenues of compliance are noted here.
A layout of the aircraft may be used to evaluate compliance with § 27.783(b). The main rotor should have sufficient clearance to allow a typical person to stand upright, outside, near the door or doors. The auxiliary rotor should be located as far as practicable from any passenger doors. Appropriate instructions for entering or Par 335 415
leaving the rotorcraft may be furnished in the flight manual, placards, or equivalent to further reduce possible hazards. Tail rotor marking standards are referenced in Paragraph 751 of this advisory circular.
(ii) If necessary, a door and engine or rotor system interlock system may be employed to prevent opening of the door with the rotors operating. Other systems may be used. In case of emergency, the system must allow opening of the door (exit) from inside or outside the rotorcraft.
335A. § 27.783 (Amendment 27-26) DOORS.
a. Explanation.
(1) Each closed cabin should have at least one door. A door on the opposite side of the cabin may be used to also comply with the exit requirement of § 27.807.
(2) Amendment 27-26 extends the requirements of § 27.783 to:
- include each external door, not just passenger doors; and,
- require provisions of door location and procedures to protect persons from danger from propellers, engine intakes, and engine exhausts.
b. Procedures. All of the policy material pertaining to this section remains in effect. In addition:
(1) Occupants of the rotorcraft and servicing personnel should be protected from possible injury when using any external door to enter or egress the rotorcraft and when loading cargo or servicing the rotorcraft. Consideration should be given to door location and operating procedures to include protection from propellers (if equipped) and engine inlets and exhausts, as well as from rotors.
(2) These new requirements clarify that engine exhausts, engine inlets, and propellers, as well as rotors, are potentially hazardous and should be located or designed to protect rotorcraft occupants and ground personnel.
(3) Door operating procedures, including readily visible markings, should be provided to minimize possible injury to personnel when practical component locations or component design features, alone, do not assure freedom from possible injury.
336. § 27.785 (Amendment 27-21) SEATS, BERTHS, SAFETY BELTS, AND HARNESSES.
a. Explanation.
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(1) The standard concerns occupant seat and berth (litter) devices and restraint of the occupant (170-pound weight) for specified conditions. The occupants shall be restrained and protected for flight, landing, and the emergency landing conditions specified in § 27.561(b). This standard and § 27.561 have the objective of providing each occupant with every reasonable chance of escaping serious injury for the stated conditions.
(2) The standard includes both serious (general) injury, Paragraphs (a) and (e), and head injury, Paragraph (b). Furthermore, Paragraph (b) requires certain design features or practices for head injury protection.
(3) The pilot seats shall additionally withstand the pilot control effort forces stated in § 27.397.
(4) Seat or berth static test or structural analysis conditions (which are procedures) were previously stated but removed by Amendment 27-21.
b. Background.
(1) FAR Part 27 through Amendment 27-20 and its predecessor, CAR Part 6, specified design conditions (flight, landing, and emergency landing conditions, § 27.561) for each seat and berth. Pilot seats were also subject to pilot control forces (reaction) of § 27.397. Structural strength analysis and testing could be simplified or conditions combined as stated. A factor applied to each design load shall be at least the "fitting" factor specified in § 27.625 and applied as stated therein.
(2) Amendment 27-21, adopted November 1984, expanded the standard significantly to contain objective and specific standards for improved occupant protection for flight, landing, and the emergency landing conditions of § 27.561.
(i) A shoulder harness is required for each front seat occupant. A shoulder harness (also called upper torso restraint) or other means shall be used to protect other occupants from head injury. Design features of the belt and harness are also included. A factor of 1.33 was also adopted. Protection while seated or moving about during normal flight and moderately rough air is also a part of the amended standard. This is similar to the transport rotorcraft standards.
A load distribution between the belt (60 percent) and harness (60 percent) is stated. Design standards for any head rest, if installed, are stated. A factor of 1.33 shall be applied to the design loads for the attachment of each seat to the structure and each belt and/or harness to the seat or structure and the head rest. This factor is applied whether the seat and restraint system is proven by static test or by analysis.
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(3) An AC applicable to safety belts and shoulder harnesses for small airplanes has been issued. The information in AC 23-4, "Static Strength Substantiation of Attachment Points for Occupant Restraint System Installations June 20, 1986, should be helpful in complying with § 27.785.
Dynamic impact tests may be voluntarily proposed by the applicant.
At least two conditions should be used to be representative of impact cases. Report No. DOT/FAA/CT-85/11, Analysis of Rotorcraft Crash Dynamics for Development of Improved Crashworthiness Design Criteria, June 1985, may be obtained for reference from the National Technical Information Service, Springfield, Virginia 22161.
(ii) Advisory Circular 21-22, Injury Criteria for Human Exposure to Impact, June 20, 1985, may be used for part of the acceptance levels or performance criteria in developing a proper dynamic test proposal. The static design conditions contained in the present standards shall be satisfied also.
c. Procedures.
(1) Each seat with its belts and harnesses are to be substantiated for the flight, ground, and emergency landing loads of § 27.561 by structural test or stress analysis.
Approval can be gained by Technical Standard Order (TSO) approval or by accomplishing sufficient structural substantiation to gain certification approval of the seat and its belts) and harness as part of the type design of the rotorcraft.
TSO No. C-39a concerns standards for aircraft seats, including rotorcraft seats. If TSO No. C-39a is used as an approval basis for a specific rotorcraft seat, the seat and harness should be checked to ensure it has been substantiated for the vertical (up and down) and side loads imposed by installation in the aircraft. For example, TSO No. C-39a (and NAS 809) specifies an ultimate down load of 4.0g which is in agreement with the 4.0g emergency landing load factor of § 27.561, but it may be less than the design maneuver load factor (which can be as high as 3.5g limit or
5.25g ultimate).
(i) The 1.33 factor is specified for substantiation of attachments of each seat to the structure and each safety belt or harness to the seat or structure and the head rest, if used, for § 27.561 loads, whether analysis or test is used.
(ii) If static testing of seats, belts, and harnesses is used, the body block of NAS 809 may be used. The corners of the NAS 809 body block may be radiused and padded if it is found that the small radii cause premature, unrealistic crippling of thin wall tubing or other structure used in the static seat.
(iii) The substantiation of the pilot seats is required to include pilot forces of § 27.397 in conjunction with normal flight and ground loads. For example, the pilot foot force (195 pounds ultimate) must be reacted by the seat.
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(2) The head rest, if used, shall be substantiated for a head weight of 13 pounds, § 27.561 inertia load factors, and a factor of 1.33 whether by test or analysis.
(3) The following criteria have been found satisfactory for preventing occupant head injuries:
(1) Whenever a harness is used, it should support the shoulders without applying hazardous loads to the side or front of the neck. It should be easily donned and removed. A single point release with the seat belt is required for each pilot's seat and preferred for other seats. If a separate release is provided, it must be simple, compatible with the seat belt release, and near the seat belt release. The harness should be tested in conjunction with the seat belt using a "body block" similar to that of NAS 809, if possible. It shall be tested to 60 percent of the § 27.561 minor crash loads for the entire occupant weight of 170 pounds. TSO-C114, Torso Restraint Systems, dated May 27, 1987, was recently issued.
(il) During certification TIA testing, the pilot shall ensure that all of the pilot's necessary functions may be performed with the seat in the most adverse adjustable position and the belt and harness fastened. Each belt and harness shall also be secured, when not used, if necessary, to comply with § 27.785(c).
(Ill) Elimination of injurious objects within striking distance of the head and other vital parts can be accomplished by removal of objects with sharp edges or rigid surfaces from within striking distance of vital parts of the occupant. Dimensions and weights for typical occupants are available in U.S. Army USAAVLABS Reports 70-22 (August 1969) and 66-39 (June 1966) and NACA Report TN 2991 (August 1953).
Because of the range of occupant head striking distance, a combination of "elimination of injurious objects" and "cushioned rests" may be required for some interior configurations. If only a belt or a belt-harness which allows use of only the belt is installed, the minimum arc or strike sphere requirement may be met by establishing a 35-inch minimum radius strike-free zone from the seat back and bottom cushion junction. The cushions may be assumed to be normally compressed.
(iv) An acceptable cushioned rest can be provided by use of a 1-inch thickness of foamed polyvinyl chloride (PVC) or equivalent energy absorbing material.
The density of material should be in a 5- to 10-pound per cubic foot density range.
PVC foam has the property of absorbing energy efficiently with negligible rebond effects. PVC foam recovers slowly to the original configuration after deformation. If PVC foam is used, however, care must be taken in its application relative to its flammability characteristics (reference § 27.853).
(4) Handholds for the occupants are generally provided by transport aircraft seat backs adjacent to the aisle. If the seat backs fold, the amount of support provided by the seat backs before they fold must be evaluated in a furnished interior or mockup.
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To provide adequate support, the seat back may use an easily disengaged latch or adequate friction in the hinge mechanism to obtain adequate support. Handholds along the aisle are, of course, not needed for rotorcraft with no aisles or where seat belts must be fastened during flight according to the operating rules.
(5) Projecting objects which could injure occupants in normal flight should be padded. The amount of padding required depends on the location, size, and minimum radius of the projecting object. In general, this requirement may be met by padding sharp edges with one-half inch of PVC foam or equivalent energy absorbing material (5 to 10 Ibs. density). Objects with edge radil in excess of 1 inch may meet the requirements of § 29.785(e) with a lesser amount of energy absorbing padding, if it can be contacted only by persons while "seated or moving about in the rotorcraft in normal flight."
336A. § 27.785 (Amendment 27-25) SEATS, BERTHS, SAFETY BELTS, AND HARNESSES.
a. Explanation.
(1) The title of § 27.785 now includes berths (which would include litters).
(2) Section 27.785(a) has been revised to include reference to the new § 27.562, "Emergency Landing Dynamic Conditions"
(3) Section 27.785(b) has been revised to include a reference to the new § 27.562(c)(5) head injury criteria and to describe a torso restraint system that is contained in TSO-C114.
(4) Section 27.785(f) has been revised to change the percentage of load distribution of a combined safety belt and harness from 60-60 to 60-40.
(5) A new § 27.785(i) has been added which provides a list of "seating device system" components.
(6) A new § 27.7850) provides for deformations of the seat energy absorption device system installed to meet the requirements of § 27.562 but requires that the system "remain intact and not interfere with rapid evacuation of the rotorcraft." Further "structural" performance standards are contained in §§ 27.562(c)(1) and (2).
AC 20-137 also contains information.
(7) A new § 27.785(k) provides static strength and restraint requirements for litters and berths. Litters may be oriented laterally as well as longitudinally in the rotorcraft. Dynamic tests of litters are not required. For longitudinally oriented litters, features should be provided to protect the occupant from the increased loads in § 29.561(b) of Amdt. 27-25.
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7/30/97 • AC 27-1A
b. Procedures. The procedures of Paragraph 336 still apply to static substantiation of the seats, berths, safety belts, and harness. In addition:
(1) Compliance with § 27.562 (except litters are not included) and § 27.561(b) is required.
(2) Section 27.562 includes a specific pass fail criteria, which includes head injury criteria (reference AC 20-137).
(3) Shoulder harnesses need only be substantiated for 40 percent of total occupant load rather than the former 60 percent adopted by Amendment 27-21.
(4) AC 20-137 provides guidance for evaluating the functioning of a seating energy absorption device system under dynamic test conditions. Stroking is generally associated with the vertical-horizontal impact case and is recognized in the static strength substantiation.
(5) Berths or litters installed within 15° or less of the rotorcraft longitudinal axis (oriented longitudinally) shall use a combination of restraint devices, such as a padded end-board, cloth diaphragm, or equivalent means to withstand and distribute the occupant loads resulting from § 27.561(b) requirements. Other berths or litters may be equipped with straps or safety belts to withstand the forward reaction of § 27.561(b) as well as other loads, including flight loads.
Berths/litters may be substantiated by static load tests, analysis, or a combination thereof and need not be substantiated to the 1.33 fitting factor of seat installations.
(її) The berth/litter occupant's head, neck, and spine should be protected from (landing) impact forward loads by appropriate design means; e.g.,
• non-longitudinal orientation of the berth/litter; or
• "feet forward" orientation; or
• distribution of an appropriate percentage of forward loads on the shoulders (not solely to the head and spine).
(iii) Recommendations for litter occupant
• If the occupant's head is oriented forward, a shoulder harness should be provided, in conjunction with body and leg straps, that prevents the occupant's head from falling off the litter. A padded Par 336A 421
end board, diaphragm, etc., may be used, provided head and spinal loads are alleviated or prevented.
• If the occupant's feet are oriented forward, the padded end board may also be used in combination with body and leg straps or other such restraints.
• Multiple or combinations of devices should be used to distribute the occupant loads as well as protect the occupant from possible neck and spine compression.
337. § 27.787 (Amendment 27-11) CARGO AND BAGGAGE COMPARTMENTS.
a. Explanation.
(1) This standard concerns the strength or structural integrity of either a cargo or baggage compartment. For purposes of this paragraph, baggage and cargo compartments are synonymous. Other design standards are also included.
(2) Fire protection standards of these compartments are contained in § 27.855, Paragraph 359, of this document.
(3) The compartment must contain the maximum (design) weight cargo for maximum landing and flight load factors. The minor crash conditions noted in § 27.561 are not applied to cargo compartments. However, a forward ultimate load factor of 4 is applied to the contents of cargo compartments. This forward load condition is related to occupant protection. Compartments forward of the occupant's compartment may be designed to the appropriate landing load factor (landing with drag and side load).
(4) Features such as straps, nets, ropes, and possibly other means of restraint may be used when necessary to prevent hazardous shifting of cargo as prescribed under flight and landing loads.
(5) Compartment lamps must be protected from possible lamp bulb and cargo contact.
(6) Other than the standards in this section, specific standard design features for cargo compartment doors are not contained in FAR Part 27. The following are recommended design features.
Door latch or lock mechanism should not fail and allow the door to open and should not open as a result of cargo shifting.
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(її) Crewmembers should by visual means such as handle positions and markings determine, when on the ground, that the door is fully locked. A separate signal system may also be used to show a door unlatched condition.
(7) Compartment marking standards such as maximum weight, floor loading, possible tiedown instructions and other appropriate compartment markings or placards are prescribed in § 27.1557(a).
b. Procedures.
(1) The compartment design allowable load, including distributed loading, is determined during the initial design phases of the rotorcraft. For an example, the compartment may have a placarded maximum allowable load of 250 pounds, with an allowable distributed load of 100 pounds per square foot. The compartment maximum load and floor distributed load (allowable pounds per square foot) should be included in a stencil, placard, or equivalent durable marking per § 27.1557(a).
(2) Static tests or analyses may be used for substantiation. Light weight rotorcraft configurations typically should be associated with the most severe flight and landing load factors.
(3) Structural substantiation of the fuselage for flight and landing loads must include the baggage and cargo restraining devices and associated attachment structure. Structural substantiation of the compartment structure must include the 4g ultimate forward load condition of § 27.787(c) in addition to the flight and landing load conditions. These can be handled as separate conditions if the structure is substantiated by analysis. If static tests are conducted, all load conditions must be accounted for. A test plan should be approved and conformity inspections conducted prior to FAA/AUTHORITY witnessing of tests.
(4) Cargo nets or straps installed for compliance with § 27.787(b) must be substantiated for the maximum flight and landing loads. The forward load condition of § 27.787(c) must be proven also. Nets or straps should be adjustable.
(5) Lamp bulbs should be guarded, recessed, or placed in upper inside corners and guarded to prevent contact with cargo and possible bulb breakage or excessive heat.
(6) If the door design recommendations in 337a(6) are accepted, these features should be confirmed by design data review and during a compliance inspection. Index or alignment marks with respect to handle (door locked) position are also recommended. If a signal system is used, a switch at the door latch that would signal "door open or unlatched" to the flightcrew is recommended.
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