SUBPART D - DESIGN AND CONSTRUCTION FLOATS AND HULLS.
AC 27.751 § 27.751 (Amendment 27-2) MAIN FLOAT BUOYANCY.
a. Explanation.
(1) The 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 27-2) 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 at operating pressure of each float is used) should be a minimum of 50 or 60 percent greater than the maximum certificated weight of the rotorcraft.
(2) Capsizing.
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, that is ineffective.
(•) 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.
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AC 27.753 § 27.753 MAIN FLOAT DESIGN.
a. Explanation. Loads and load distributions are specified for float design as follows:
(1) Bag floats are to be designed for:
(1) The maximum pressure differential developed at the maximum design altitude.
(ii) The vertical loads prescribed in § 27.521(a) distributed over three-fourths of the bag's projected area.
(2) Rigid floats are to be designed for vertical, horizontal, and side loads prescribed in § 27.521 distributed along the length of the float.
b. Procedures. Structural substantiation may be accomplished by static tests or analyses using the specified loads. Substantiation should cover the float and float attachments.
AC 27.755 $ 27.755 HULLS.
a. Explanation.
(1) The section requires amphibious rotorcraft with a single hull (main float design) and with auxiliary floats (outriggers) to provide a margin of positive stability great enough to minimize the probability of capsizing when any single (usually the most critical) compartment is flooded. Landing gear wheel tires may be used for stability purposes as well.
(2) Limitations for water operation are not intended by this section, but information for water operation must be included in the rotorcraft flight manual.
(3) Wave height or sea state and buoyancy relative to fresh water is not specified but is encompassed in the objective statement of § 27.751(b).
(4) Section 27.751 specifies an excess buoyancy requirement of 50 percent for single main floats (hulls) and contains a capsize/stability standard also. This section complements § 27.755 for certain hull designs.
(5) Sections 23.751, 23.755, and 23.757 concern design standards for small airplanes and may provide insight into possible rotorcraft hull designs.
b. Procedures.
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(1) The main hull must have multiple compartments. Assuming the hull has 50 percent excess buoyancy capacity, six to ten sealed compartments of approximately equal volume would allow loss of one with at least 25 percent excess capacity remaining. However, the attitude of the rotorcraft is critical with respect to capsize stability, and additional compartments may be necessary.
(2) The designer must consider separately the loss of buoyancy for each critical compartment, the aircraft center of gravity, and attitude in the water for the appropriate sea state or water height. Sea state 4, moderate, as noted in figure AC 27.801-1, is acceptable.
(3) The auxiliary floats (outrigger) must have multiple compartments. In addition, wheel tires may be used as a compartment if applicable to the design.
(4) For each critical condition under consideration, a single compartment for either the main hull or auxiliary float should be flooded or collapsed. Combined failures, one in each, are not required.
(5) Model stability (or capsize) tests are encouraged to demonstrate compliance with this section.
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SUBPART D - DESIGN AND CONSTRUCTION
PERSONNEL AND CARGO ACCOMMODATIONS AC 27.771. § 27.771 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 expected range of 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. 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, tans, and gyros should not have noise or vibration characteristics which could contribute to pilot fatigue or distraction. Instrument panel vibration is specifically addressed in § 27.1321.
b. Procedures. 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 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.
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AC 27.773. § 27.773 (Amendment 27-48) PILOT COMPARTMENT VIEW.
a. Explanation. The section outlines requirements for pilot view in fairly general terms. Requirements are purposely less stringent than for transport category rotorcraft to allow for cockpit designs ranging from fully enclosed to open to the elements. Section
27.773(b) was changed at amendment 27-48 to include the option for a ground test in lieu of a night flight test. Paragraph b. (2) below contains guidance to reflect this change.
b. Procedures.
(1) The following procedures are one acceptable means of evaluating pilot compartment field of view considering only those objects in the pilot compartment and 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 merit. 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, a pilot and copilot, is required, the 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 27.773-1 needs only to comply to 60° left, and the copilot's area of visibility to the right 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 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 comply 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 0.9VNE 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.
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(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 of the distance which exists between the eyes, or 1 ¼ inches. With the referenced eye position located as indicated in paragraph AC 27.773b.(1)(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 27.773-1.)
(A) 20° forward and above the horizon between 0° and 100° left.
(B) 20° forward and below the horizon between 10° and 100° left.
(C) 20° forward and below the horizon at 10° left increasing to a point 30° forward and below the horizon at 10° right.
(D) 50° forward and below the horizon between 10° right and 135° right.
(E) 20° forward and above the horizon at 0° increasing to a point 40° above the horizon at 80° right and 100° right and then decreasing to a point 20° forward and above the horizon at 135° right.
(iii) Any vertical obstruction which falls within the minimum area of visibility outlined in paragraph AC 27.773b.(1)(ii) should be governed by the following:
(A) Between 20° right and 20° left--no vertical obstruction.
(B) Between 20° right and 135° right -- no vertical obstruction greater than 2.5 inches in width.
(C) Between 20° left and 100° left -- no vertical obstruction greater than
2.5 inches in width.
(iv) Any horizontal obstruction which falls within the minimum area of visibility outlined in paragraph AC 27.7736. (1)(il) should be governed by the following:
(A) The area 15° forward and above the horizon between 135° right and 40° left decreasing to a point 10° above the horizon at 100° left, and 15° forward and below the horizon between 135° right and 100° left should be free from horizontal obstructions.
(B) The area above and below the horizon which is between the minimum area of vision specified in paragraphs AC 27.773b. (1)(ii) and AC
27.773b. (1) (iv)(A) is limited to one horizontal obstruction above and one below the horizon. These horizontal obstructions should not be greater than 4 inches in width. An overhead window which will provide twice as much additional visibility as that lost due to the obstruction should be located immediately above any obstruction above the horizon.
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This requirement is in addition to any area of visibility specified by paragraph AC
27.773.(b)(2)(i) which may be included in the overhead window area.
(C) If the instrument panel obstructs any required area between 10° left and 10° right below 20° forward and below the horizon, a window which affords triple equivalent additional visibility should be located immediately below and between the angles of 20° left and 20° right above 65° below the horizon.
(v) For steep rejected takeoffs and steep approaches (such as to oil rigs or confined heliports), the visibility should be such that the pilot can see the touchdown pad and sufficient additional area to the side and forward to provide both an accurate approach to the touchdown point as well as a satisfactory degree of depth perception. A 5-inch head movement by the pilot forward and/or sideward of the normal position is acceptable in determining compliance.
(2) 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." Assess glare from reflected light to ensure that it does not reflect into the pilots' eyes. Assess reflections of pilot or cockpit structures off of instrument glass that may interfere with the readability of displays or instruments. This problem is most apparent in IFR equipped aircraft (having larger instrument panels and avionic consoles) operating in VER utility roles.
If night approval is requested, then compliance with 27.773 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.
(i) 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 AC27.773-1 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.
(il) 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 and reflections D - 65
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.
(3) Moderate rainfall is defined by the National Weather Service as an accumulation of between 0.01 and 0.03 inches in 3 minutes. Since the rule effectively permits open cockpits, a determination of what would unduly impair the pilots' view in moderate rainfall is obviously very subjective. If it is established that rain removal systems are necessary, those systems may be evaluated on the ground with a hose, but they should also be assessed in flight under applicable conditions. Obscuration of side windows by rainfall should be addressed, particularly for confined area approaches. The need for windshield wash systems should be assessed if the aircraft will be used in an offshore salt-spray environment.
(4) If icing certification is requested, a means must be provided to ensure that a sufficiently large viewing area is kept clear of ice to permit safe operation. As a minimum, a clear area on the windshield should be available, although some configurations could require a clear view in other areas to provide an adequate level of safety in certain operations. Systems provided to ensure a clear view in icing conditions should be evaluated during icing flight tests.
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9/30/99
THIS AREA
LIMITED TO ONE
HORIZONTAL DESTRUCTION (NOT GREATER THAN 4 INCHES IN WIDTH) 20° PRET OF WOR (CENTRALASS) _ ZERD REFERENCE
FILOT VIEW FOR NO HORIZONTAL OESTRUCTIONS CREW/OF ONE 7 95 7 BETWEEN DASHUNES, FT 20ª
THIS AREA LIMITED TO ONE HORIZONTAL OBSTRUOTION 40º (NOT GREATER THAN 4 INCHES IN WIDTH) (NOTE: PILOT IN COMMAND IS CONSIDERED
TO OCCUPY RIGHT-HAND BEAT) тоbs 80° 60° 40° t0° 0° 1o" 40º 135ª 60° 80ª †00° 120°
• VERTICAL OBSTRUCTIONS • NO VERT. VERTICAL OBSTRUCTIONS UMITED TO 2,5 INCHES IN WIDTH OESTRUCTIONS LIMITED TO 2.5 INCHES IN WIDTH FIGURE AO 27.773-1, COCKPIT VISIBILITY Page D - 67 AC 27-1B
AC 27-1B, Chg 2 4/25/06 AC 27.775 § 27.775 WINDSHIELDS AND WINDOWS.
a. Explanation. The use of nonsplintering safety glass is specified when glass is used in windshields and windows 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, epoxies, etc. The glass selected should 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.
AC 27.775A § 27.775 (Amendment 27-27) WINDSHIELDS AND WINDOWS.
a. Explanation. Amendment 27-27 changed § 27.775 to allow the use of materials other than nonsplintering safety glass; i.e., plastics are allowed. Additionally, whatever material is used should not break into dangerous fragments upon impact.
b. Procedures. The procedures contained in paragraph AC 27.775 apply equally to glass or plastics.
AC 27.777 $ 27.777 COCKPIT CONTROLS.
a. Explanation. This section defines the general cockpit control requirements.
Cockpit control location and arrangement with respect to the pilot's seat must be designed to accommodate pilots from 5'2" to 6'0" in height. Pilots within this range should be able to reach and operate all required controls and have sufficient clearance with the structure, panels, etc.
b. Procedures.
(1) The applicant should have a cockpit design report which documents the anthropometric suitability of the cockpit. Subsequent cockpit evaluations of control movement and location should be conducted with adjustable seats and/or controls positioned in a flight position for the subject pilot. Essential controls should be evaluated with the shoulder harness locked in the retracted position. Evaluation pilots should be aware of their individual anthropometric measurements and temper their assessments based on this information. Ideally, a new design should include evaluations by a range of different sized subject pilots. Control considerations for a second pilot position are the same as for the pilot station. Paragraph AC 27.771 discusses current philosophy concerning duplication of controls.
(2) As background, the following are examples of cockpit control issues which should be avoided:
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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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