foot-pounds at the design landing rate of absorption. The design takeoff and landing weight and rotorcraft speed in knots for brake application are a part of the equation.
The brake manufacturer should furnish this rating and the two noted parameters for the selected design or designs. The ratings of selected brakes should be included in a structural design data report such as a design criteria report. The use or application of each brake design on the particular rotorcraft design should not exceed capacity of the brake or the ratings established under the TSO. If appropriate, the part number and manufacturer of each brake may be listed in the structural data reports as well as listed in the type design drawings.
(2) The limiting brake torque obtained from the brake manufacturer should be used in complying with §§ 29.493(b)(2) and 29.497(g)(2)(ii).
(3) Compliance with the brake standards should be confirmed, demonstrated, and recorded as a part of the flight test type inspection report. This applies to TSO brakes and to brakes approved as a part of the aircraft type design.
(4) If found necessary under the provisions of § 29.771, the second pilot station should have brake control devices. The brake control devices should be listed with the other required equipment that defines the equipment necessary for a second pilot station.
(5) A brake assembly may be evaluated and approved under Part 29 as a part of the aircraft type design. TSO -approved brakes are not specifically required but are recommended. For non- TSO-approved brakes, all detail and assembly drawings, required test proposals, and test results reports may be submitted and processed as a unique part of the particular aircraft type design.
(6) During an inspection of the landing gear, such as an engineering compliance inspection, the brake location should be checked to ensure the brake does not contact the ground when the tire is deflated. Type design drawings should control the proper location of the brake on the landing gear.
AC 29.737. § 29.737 SKIS.
a. Explanation. This st andard is, in part, derived from small airplane standards.
Aircraft skis approved under TSO-C28 may be used on rotorcraft. TSO -C28 for aircraft skis refers to Sections 4 and 5 of National Aircraft Standards Specification 808, dated December 15, 1951, for strength and performance standards. The standard also addresses flight/aerodynamic loads.
(1) A maximum limit load rating is assigned to each ski approved under TSO-C28.
(2) This limit load rating must not be exceeded by the maximum limit ground load determined under the standards of § 29.505, Ski landing conditions.
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(3) The ski installation is also subject to the maximum aerodynamic and inertia loads and to the ground rotation or torque load per § 29.505(c).
(4) Ski mounting or installation parts used in the particular application are subject to substantiation as any landing gear member is subject to substantiation.
(5) Ski installations are also subject to flight and ground operation evaluations.
(6) Pads or “bear paws” on skid or wheel landing gears for use in snow or soft soils are unique to rotorcraft. These shall be approved also. For new type certificate applications after November 27, 1989, § 29.571, Amendment 29-28 requires fatigue substantiation of the landing gear. The effect of pads, etc., shall be evaluated in compliance with the standard.
b. Procedures.
(1) The limit load rating for the ski selected shall be obtained from the ski manufacturer. This information shall be included in the design criteria and/or structural substantiation reports. The type design drawings will include the appropriate part number for the TSO-approved product and the necessary installation information.
(2) The design limit loads derived in compliance with § 29.505 shall not exceed the ski limit load rating. The skis shall be substantiated for the torque load in § 29.505(c) since the TSO standard does not contain a similar requirement.
(3) Skis that are not TSO approved may be approved as a part of the aircraft type design by complying with the strength and performance standards contained in TSO-C28 (NAS 808).
(4) The aerodynamic loads shall be based on a limit load design speed of
1.11 VNE. The maximum V NE used in design may be reduced only for a “ski configuration” airspeed limitation.
(5) Pads or “bear paws” installed on skid or wheel landing gear to facilitate operations in snow conditions or marsh lands may be approved as a part of or as an alteration to the aircraft type design. Rational flight and landing design loads applicable to the particular pad design must be developed and strength substantiating data submitted proving compliance with the strength and performance standards contained in Part 29. In addition, skid landing gear may be subject to excessive vibratory loads while in flight whenever the weight and mass distribution is altered by adding “bear paws.” The effect of additional weight should be investigated over the flight operating regimes, including the approved range of rotor speeds. Resonant vibratory conditi ons should be avoided or highly damped, thus avoiding a potential change in service life. In compliance with § 29.571, Amendment 29-28, stress measurement, etc., may be necessary, if the standard is applicable.
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SUBPART D - DESIGN AND CONSTRUCTION FLOATS AND HULLS.
AC 29.751. § 29.751 (Amendment 29-3) MAIN FLOAT BUOYANCY.
a. Explanation.
(1) This section specifies standards for single and multiple float buoyancy in fresh water. The standard does not apply to ditching/emergency flotation devices, but to amphibian rotorcraft devices.
(2) It is a design and a performance standard. Rigid or inflatable floats may be used. Enough water tight compartments (per Amendment 29- 3) rather than a specific number are required to minimize the probability of capsizing when one compartment is flooded or deflated.
b. Procedures.
(1) Excess buoyancy. A minimum of 50 or 60 percent in excess of the maximum certificated weight of the rotorcraft is required for single or multiple floats, respectively. The weight of fresh water (density 62.42 pounds per cu. ft.) displaced by fully submerged float or floats (total volume of each float at operating pressure is used) should be a minimum of 50 or 60 percent greater than the maximum certificated weight of the rotorcraft.
(2) Capsizing.
(i) Each float should have enough sealed, separate and approximately equal volume compartments to minimize the probability of capsizing when the critical compartment is flooded or deflated. Five or more compartments in each float are usually necessary to meet the standard. Ten compartments per float have been employed in certain designs.
(ii) An analysis or test or combination thereof may be used, if necessary, to prove a positive margin of stability with the most “critical” compartment in one float flooded or deflated.
(iii) The location of the floats, and the most critical compartment, the rotorcraft weight, mass moment of inertia, and center of gravity location are also important considerations for capsize stability.
AC 29.753. § 29.753 MAIN FLOAT DESIGN.
a. Explanation .
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(1) Strength or design load standards are encompassed in the standard for inflatable bag and rigid floats. Bag pressure loads are included. The standard applies to an amphibious rotorcraft.
(2) The float landing loads are derived from the drop test of the float landing gear, or the load may be derived from tests of the wheel (or skid) landing gear (reference § 29.521). Bag type floats are not subject to the side loads according to the standard. Rigid floats, whether single or dual, are subject to the side load in each direction.
(3) Inflatable bag type floats should also be designed for the maximum pressure differential developed for the maximum operating altitude difference requested. That is, the resulting pressure difference between an operational altitude and a take-off site elevation should be established, and proven and may become an operating limitation.
(4) Landing loads suffice for the aerodynamic loads for typical rotorcraft float designs. Nonetheless, design and/or support of the forward part of bag type floats should be evaluated for maximum design speeds to prevent collapse or significant distortion of the bag while in flight.
(5) Resistance to puncture and abrasion at attach/wear points is not in the standard but is an important design consideration. “Girt” or attachment design loads shall be sufficient to withstand the loads imposed by the standards.
(6) The water or sea conditions (wave heights) evaluated in §§ 29.231 and
29.239 tests are not limitations but should be noted in the procedures section of the flight manual.
(7) The standard does not apply to ditching/emergency floatation devices.
b. Procedures.
(1) Landing load factor.
(i) A drop test of the float landing gear may be conducted to obtain the limit landing load factor (reference § 29.725). Level landing attitude should be used for the float assembly.
(ii) The limit load factor for wheel or skid landing gear may be used (reference § 29.521) for the floats.
(iii) The float design ultimate load factor is 1.5 multiplied by the limit load factor.
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(2) Flight aerodynamic loads--bag type floats.
(i) Evaluate collapse or significant distortion of bag type floats for speeds up to VD (1.11 VNE) with the minimum operating bag pressure.
(ii) External tubes to support the bag may be employed.
NOTE: Design landing loads may exceed the flight loads.
(3) Altitude differential loads.
(i) Bag type floats should not rupture due to the change in absolute pressure from take-off to the operating altitude. The applicant should select and prove the maximum operating altitude differential desired. A 5,000 to 8,000 feet operating differential may be a sufficient limitation. That is the rotorcraft with bags properly inflated could not operate more than 5,000 to 8,000 feet above the take-off site elevation.
(ii) A proof and ultimate pressure test should be conducted for the design.
If operating or inflation pressure is 2.62 PSI (including a tolerance) and 5,000 feet (pressure) differential is desired (use sea level to 5,000 feet pressures), the proof or limit pressure should be 2.62 + 2.47 = 5.09 PSI. The pressure relief valves may be set at this value also. The change in size during inflation should be recorded. Significant changes may adversely affect flight characteristics and should be evaluated. The ultimate or burst free pressure should be proof pressure (5.09 PSI) multiplied by 1.5 or
7.635 PSI. A video or photographic record may be used as a reference of the change in size or shape for this test.
(iii) Each compartment should be equipped with a pressure relief valve to further protect the bag from excessive internal pressure.
(iv) At least one float should be subjected to a burst pressure test.
Record the gauge pressure of burst.
(4) Landing loads.
(i) Rigid float vertical and a combined vertical and aft load conditions. A vertical or up-load only and a vertical combined with an aft load component for a resulting vector angle of 14.03° from the vertical axis of the rotorcraft shall be used.
Reference § 29.521(a). The resulting design load is the same load in both cases.
(ii) Rigid float side and vertical load condition. For each rigid float, whether single or dual, a vertical load combined with a side load resulting in a vector angle of 26.6° from the vertical axis of the rotorcraft shall be used. The side load is applied to each float individually. Both inward and outward acting side load conditions shall be substantiated separately for the design of dual floats.
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(iii) Load distribution on rigid floats shall be appropriate for the critical conditions. ANC -3 or § 25.533 and FAR Part 25, Appendix B may be useful.
(iv) Bag type float. The loads and the distribution of the loads are rather simple according to the standards. Only vertical loads and vertical with aft (drag) component are specified in the standard. These shall be distributed along the length over 75 percent of the projected area of the bag. Side loads are not required.
(5) Operating limitations.
(i) VNE with floats installed is typically lower than the VNE for wheel or skid landing gear rotorcraft configurations.
fittings.
(ii) Bag inflation pressure shall be placarded or stenciled near inflation
(iii) The operating attitude differential proven for bag floats shall be an operating limitation. In addition, the flight manual should caution pilots about the effect of a significant decrease in altitude from the take off level which causes or reduces pressure in the bag. Placards may be employed as well.
(iv) Flight test results may dictate a further reduction in VNE or changes in other operating limitations.
AC 29.755. § 29.755 (Amendment 29-30) HULL BUOYANCY.
a. Explanation.
(1) This section contains performance standards for an integral fuselage hull and auxiliary (such as outrigger) floats. Water -based, amphibian and limited amphibian rotorcraft were encompassed in the standard.
(2) Amendment 29-3 added but Amendment 29-30 removed paragraph (b) which concerned Limited Amphibian Rotorcraft. Rotorcraft of that type used a “boat type hull” which is not desirable now and are certificated to the standards of § 29.801, Ditching, and § 29.563, Structural ditching provisions. (Limited amphibian rotorcraft were converted to the ditching configuration.)
(3) The worst combination of wave height and surface winds selected by the applicant shall be used in compliance with the standard.
b. Procedures.
(1) Capsizing.
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(i) The hull and auxiliary floats shall have enough sealed compartments to allow failure of the critical, single, compartment in either the hull or auxiliary float and minimize the probability of capsizing.
(ii) Location of the most critical compartment (whether hull, sponson, or auxiliary), rotorcraft weight, mass moment of inertia, and CG location are also important considerations to prove stability or not capsizing.
(iii) The lightweight rotorcraft configuration and wind and wave condition should be considered, as well as the heavy weight configuration.
(iv) The sea state (worst combination of wave height and surface winds) is selected by the applicant. The condition proven is included in the procedures or information section of the flight manual. (It is not an operating limitation.)
(2) Buoyancy.
(i) Excess buoyancy is necessary to comply with the standard but the amount is dependent on several factors, such as number, size, and location of the sealed, watertight, compartments.
(ii) Wheel tires may be used for buoyancy if appropriate to the design.
(iii) Fuel tanks, if properly located and protected from potential rupture and if the aircraft has a system to rapidly empty the tanks, may be used also for buoyancy.
(iv) Buoyancy may be determined using the displacement of fresh water, with 62.42 pounds per cubic ft. density.
(3) Tests.
(i) If necessary, scale models may be used to prove the stability of the rotorcraft design for the sea state and wind conditions selected by the applicant.
(ii) The rotorcraft is subject to water tests per § 29.231. Compliance with part of this standard may be demonstrated or proven for the sea state or wave height, and wind conditions selected in conjunction with the TIA flight test program. This information is not an operating limitation.
(iii) Proposals should be submitted for evaluation.
AC 29.757. § 29.757 (Amendment 29-3) HULL AND AUXILIARY FLOAT STRENGTH.
a. Explanation. The standard is an objective or performance strength standard.
The water loads in § 29.519 shall be imposed for the hull and auxiliary floats in a Page D - 65
conservative manner. The hull and float are “rigid” conventional amphibian or water-based aircraft structures.
b. Procedures.
(1) The water loads and conditions specified in § 29.519 shall be used. The pressures or load distributions should be appropriate to the design. ANC -3 and §§ 25.523 through 25.535 and Appendix B to FAR Part 25 may be of use.
(2) The water loads and applications of the loads are objective standards. A proposal and early discussions in the life of a project should be used to agree on an appropriate avenue or means of compliance. Tests or analysis supported by tests may be appropriate.
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SUBPART D - DESIGN AND CONSTRUCTION
PERSONNEL AND CARGO ACCOMMODATIONS AC 29.771. § 29.771 (Amendment 29-24) PILOT COMPARTMENT.
a. Explanation.
(1) Volumes have been written on human factors and their contribution to pilot workload and fatigue. This document cannot begin to address the myriad of considerations involved in pilot compartment design. The intent of the rule is simply to ensure that reasonable human factor engineering practices have been followed.
Equipment should be logically grouped within the pilot’s reach and view and be easy to operate. Seats should provide a reasonable level of comfort for the normal anthropometric range of pilots for a typical mission duration. Environmental considerations such as radiation from the sun through overhead windows should be addressed. Heating, cooling, and ventilation systems should be adequate for the range of expected operating conditions.
(2) Each pilot compartment and its equipment should allow the minimum flightcrew to perform their duties without unreasonable concentration or fatigue. If there is a provision/requirement for a second pilot, his station should be equipped with primary flight controls and have easy access to powerplant controls. Duplicate wheel brakes are recommended. Duplication of miscellaneous controls such as idle detent switches, RPM beep functions, nosewheel locks, and parking brakes has not been required. The need for duplicate instruments for the second pilot tends to be a function of cockpit size and panel configuration.
(3) Webster defines appurtenances as “accessory objects or apparatus.” Items such as blowers, fans, and gyros should not have noise or vibration characteristics which could contribute to pilot fatigue or distraction. Instrument panel vibration is specifically addressed in § 29.1321.
(4) Although the rule prohibits in-flight rain or snow leaks that distract the crew or harm the structure, leaks occurring on the ground should also meet these requirements. In extreme cases where an offensive leak could not be stopped, the moisture has been rerouted to a noncritical area. In the context of this rule, “structure” is interpreted to include any part of the pilot compartment to include systems and equipment.
b. Procedures.
(1) Initial evaluation of the pilot compartment should be conducted on the ground. However, the cockpit assessment should be an ongoing effort throughout the flight test program. If a second pilot position is provided/required, the adequacy of Page D - 67
controls and instruments should be evaluated under all normally expected operating conditions. If a second pilot position is not provided/required, any passenger position in the pilot compartment should be evaluated to ensure that a passenger, properly briefed by the flightcrew, can sit comfortably without inadvertent interference with normal control operations. All equipment should be operated during at least one flight of typical mission profile and duration.
(2) Although many pilot compartment rain or snow leaks can be located on the ground by dousing the aircraft with a hose, in-flight leaks often occur in varying intensity and in different locations. Flight in rain should therefore be included during flight test.
AC 29.773. § 29.773 (Amendment 29-56) PILOT COMPARTMENT VIEW.
a. Nonprecipitation Conditions.
(1) Explanation. Amendment 29-56 changed 29.773(a)(2) by adding the option to perform a ground test in lieu of a flight test. Paragraph (a)(1)(iii) below contains guidance to reflect this change.
(i) The procedures paragraph following this explanation discusses one means of demonstrating an adequate field of view.
(ii) Since glare and reflection often differ with the sun’s inclination, consideration should be given to evaluating the cockpit at midday and in early morning or late afternoon. Windshields with embedded wire heating elements should be evaluated for distortion with the system both “ON” and “OFF.”
(iii) If night approval is requested then compliance with 29.773 may be shown by either a ground or flight test. Internal lighting can be evaluated with a ground test. External lighting modifications may require a flight test. If a flight test is conducted, then the lighting system should be evaluated in likely combinations and under expected flight conditions.
(A) Internal lighting evaluations may be accomplished by a ground test with the aircraft in a dark hangar or with external light blocked to create a dark cockpit.
Locations and intensity of instrument panel and control panel light reflections should be assessed to ensure they do not interfere with the pilots’ ability to see outside the aircraft. Figure ac29.773-1 contains guidance on the areas in pilots’ field of vision where reflections should be eliminated. Although a certain amount of equipment reflection (avionics control heads, etc.) In the windshield may be unavoidable, the pilot’s normal field of view should be unobstructed. If reflections are mitigated by modifying the glare shield, then the pilots’ field of view should be revaluated. If a reflection’s effect on the pilots’ ability to see outside the aircraft is uncertain, a night flight test may be required.
(B) External lighting evaluations should be done during night flight tests. Evaluating external lights on the ground may result in unacceptable light entering the cockpit and causing reflections or glare due to reflection off the ground or surrounding structures. Landing and taxi lights should be exercised throughout their adjustment range (if applicable) to check for reflections, particularly in chin windows.
Anticollision and strobe lights should be evaluated to ensure that frequency interaction Page D-68.1
and reflections off the rotor do not result in distractions to the pilot. The effect of cabin lighting on the pilot compartment view should be assessed, particularly on EMS- configured aircraft where the in-flight use of cabin lights may be mandatory
(2) Procedures. The following procedures are one acceptable means of evaluating pilot compartment field of view considering only those objects in the pilot compartment, the windshield, and its support structure in nonprecipitating conditions.
The applicant’s design is not required to meet these guidelines, and each design should be evaluated on its own merits. The area of visibility established in the following paragraphs will provide an acceptable level of visibility for a minimum crew of one (pilot). In the event that a minimum crew of two (pilot and copilot) is required, the Page D-68.2
second pilot should have an area of visibility equivalent to that provided for the pilot but on the opposite side. In this event, the pilot’s area of visibility to the left as shown in figure AC 29.733-1 needs only to comply to 60° left, and the area of visibility for the second pilot needs only to comply to 60° right.
(i) A single point established in accordance with the provisions of this paragraph constitutes the referenced eye position (i.e., a point midway between the two eyes) from which the central axis may be located. The referenced eye position is a reference datum point based on the eye location that permits the specified vision envelope required by figure AC 29.733-1, allows for posture slouch, and is the datum point from which the aircrew station geometry is constructed. The referenced eye position should be located by means of ship’s coordinates that contain station reference number, water line, and butt line for both pilot and copilot, if applicable, and complies with:
(A) The pilot’s seat in a normal operating position from which all controls can be utilized to their full travel, by an average subject, and which should provide for vertical adjustment of the seat of not less than 2.5 inches above and 2.5 inches below this initial vertical position.
(B) The seat back in its most upright position.
(C) The seat cushion depression being that caused by a subject weighing 170 to 200 pounds.
(D) The longitudinal axis of the rotorcraft to be that of “cruise attitude”
(0.9VH or 0.9 VNE whichever is lower).
(E) The point established not beyond 1 inch to the right or left of the longitudinal centerline of the pilot’s seat.
(F) All measurements made from the single point established in accordance with this paragraph.
(ii) A dual lens camera, as photo recorder, should be used in measuring the angles specified in the paragraphs listed below. Other methods, including the use of a goniometer, are acceptable if they produce equivalent areas to those obtained with a dual lens camera. When not using a dual lens camera, compensation should be made for one-half the distance which exists between the eyes, or 1¼ inches. With the referenced eye position located as indicated in paragraph AC 29.733a(2)(i), and utilizing binocular vision and azimuthal movement of the head and eyes about a radius, the center of which is 3 and 5/16 inches behind the referenced position (this point to be known as the central axis), the pilot should have the following minimum areas of vision measured from the appropriate eye position. (See figure AC 29.733-1.)
(A) 20° forward and above the horizon between 0° and 100° left.
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