Collective control blocking the lateral movement of a pilot's leg, which in turn restricts the left lateral cyclic displacement.
(ii) Seat or seat cushion impeding the aft cyclic movement.
(IIi) Inadequate space for large feet equipped with large flight boots.
(iv) Control/seat relationship which requires unusual pilot contortions at extreme control displacements.
(v) Control/seat relationship or control system geometry which will not permit adequate mechanical advantage with unboosted controls or in a boost OFF situation.
(vi) Addition of control panels or equipment to instrument panels or consoles which restrict full control throw.
(vii) Brake pedal geometry which results in inadvertent brake application upon displacement of the directional controls.
(viii) Controls for accessories or equipment which require a two-handed operation.
(ix) Emergency external cargo release controls which cannot be activated without releasing the primary flight controls.
(x) Essential controls which cannot be actuated during emergency conditions with the shoulder harness locked.
(xi) Throttle controls which can be inadvertently moved through idle to the cutoff position.
(xii) Switches, buttons, or other controls which can be inadvertently activated during routine cockpit activity including cockpit entry.
(xili) Failure to account for operation with the pilot wearing bulky winter clothing.
(xiv) Aft cyclic movement limited by the pilot's body with a fore and aft adjustable seat in the full forward position.
AC 27.779. § 27.779 (Amendment 27-21) MOTION AND EFFECT OF COCKPIT CONTROLS.
a. Explanation. The section standardizes motion and effect of cockpit controls.
While this paragraph specifically addresses primary flight controls, engine power Page D - 69
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 (II) Down/aft = off/decrease
(iii) 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 (ti) 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 Page D - 71
AC 27-1B, Chg 3 9/30/2008 (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 collectivei 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.
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AC 27-1B, Chg 4 3/31/2014 AC 27.783. § 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, for exits other than emergency exits, provided the door instructions and markings are conspicuous.
(4) If the door is used as a "ditching emergency 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.
(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.
(6) If the door is a sliding door and intended to be opened and closed in flight, the sliding mechanism should positively attach the door to the airtrame (e.g., sliding hinge) to minimize the likelihood of the door departing the aircraft in flight. Appropriate flight limitations should also be established to minimize any hazard while operating the door.
[Section AC 27.783 continued on next page.] Page D - 72.2
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:
(i) Indicate when the door is closed and fully locked.
(її) Indicate the means of opening.
(iii) 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 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 AC 27.1565.
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(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.
AC 27.783A. § 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.
AC 27.785. § 27.785 (Amendment 27-21) SEATS, BERTHS, SAFETY BELTS, AND HARNESSES.
a. Explanation.
(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 Page D - 74
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.
(ii) 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.
(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.
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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.
(ili) 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.
(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:
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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.
(II) 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).
(#) 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.
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.
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AC 27-1B, Chg 1 2/12/03
(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 radii 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."
AC 27.785A. § 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 systemi 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).
(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.
b. Procedures. The procedures of paragraph AC 27.785 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.
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