(2) Section 27.562 includes a specific pass fail criteria, which includes head injury criteria.
(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 paragraph 27.562 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 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.
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AC 27-1B, Chg 1 2/12/03
• 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.
AC 27.785B § 27.785 (Amendment 27-35) SEATS, BERTHS, LITTERS, SAFETY BELTS, AND HARNESSES.
a. Explanation. Amendment 27-35 revised the title of the rule to now include litters to distinguish from berths. Additionally, § 27.785(k) was revised to require that the 1.33 fitting factor of § 27.625(d) must be applied to the emergency landing loads of § 27.561(b)(3) for the substantiation of attachments of each berth and litter to the structure.
b. Procedures. All of the advisory material pertaining to this section remains in effect with the following additions:
(1) A fitting factor of 1.33 must be applied to the emergency landing loads of § 27.561(b) when evaluating the berth or litter attachment and the occupant restraint system to the structure.
(2) The 1.33 factor is required whether analysis or test is used.
AC 27.787. § 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 AC 27.855.
(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.
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(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.
(i) Door latch or lock mechanism should not fail and allow the door to open and should not open as a result of cargo shifting.
(i¡) 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.
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(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 paragraph AC 27.787 a(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.
AC 27.787A § 27.787 (Amendment 27-27) CARGO AND BAGGAGE COMPARTMENTS.
a. Explanation. Amendment 27-27 adds two subparagraphs to § 27.787 (c) which clarify that cargo and baggage compartments should be designed to protect occupants from injury by the compartment contents during emergency landings. This may be done by location or by retention provisions. The new paragraphs also add a requirement that the compartment contents not cause injury when subjected to the loads of § 27.561.
b. Procedures. The procedures of paragraph AC 27.787 are still applicable. In addition to the forward load, the cargo and baggage compartment should be designed to withstand loads in other directions as specified in § 27.561. Also, the compartment may be shown to provide protection of occupants by location; i.e., cargo and baggage compartments may be shown to be located in a position where loose contents will not endanger occupants in an emergency landing impact. If the compartment is located above or behind the occupied area, § 27.561(c) may apply. If a compartment is in the occupied area, § 27.561(b) applies.
AC 27.801 § 27.801 (Amendment 27-11) DITCHING.
a. Explanation.
(1) Ditching certification is accomplished only if requested by the applicant.
(2) Ditching may be defined as an emergency landing on the water, deliberately executed, with the intent of abandoning the rotorcraft as soon as practical. The rotorcraft is assumed to be intact prior to water entry with all controls and essential systems, except engines, functioning properly.
(3) The regulation requires demonstration of the flotation and trim requirements under "reasonably probable water conditions." A sea state 4 is representative of reasonably probable water conditions to be encountered. Therefore, demonstration of compliance with the ditching requirements for at least sea state 4 water conditions satisfies the reasonably probable requirement.
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(4) A sea state 4 is defined as a moderate sea with significant wave heights of 4 to 8 feet with a height-to-length ratio of:
1:12.5 for multiengine rotorcraft with Category A engine isolation (reference paragraph AC 27 MG 3).
(i) 1:10 for all other rotorcraft.
NOTE: The source of the sea state definition is the World Meteorological Organization (WMO) Table. (See figure AC 27.801-1.)
(5) Ditching certification encompasses four primary areas of concern: rotorcraft water entry, rotorcraft flotation and trim, occupant egress, and occupant survival.
(6) The rule requires that after ditching in reasonably probable water conditions, the flotation time and trim of the rotorcraft will allow the occupants to leave the rotorcraft and enter liferafts. This means that the rotorcraft should remain sufficiently upright and in adequate trim to permit safe and orderly evacuation of all personnel.
(7) For a rotorcraft to be certified for ditching, emergency exits must be provided which will meet the requirements of § 27.807(d).
(8) The safety and ditching equipment requirements are addressed in §§ 27.1411, 27.1415, and 27.1561 and specified in the operating rules (Parts 91, 121, 127, and 135). As used in § 27.1415, the term ditching equipment would more properly be described as occupant water survival equipment. Ditching equipment is required for extended overwater operations (more than 50 nautical miles from the nearest shoreline and more than 50 nautical miles from an offshore heliport structure). However, ditching certification should be accomplished with the maximum required quantity of ditching equipment regardless of possible operational use.
(9) Current practices allow wide latitude in the design of cabin interiors and, consequently, the stowage provisions for safety and ditching equipment. Rotorcraft manufacturers may deliver aircraft with unfinished (green) interiors that are to be completed by the purchaser or modifier. These various "configurations" present problems for certifying the rotorcraft for ditching.
(i) In the past, "segmented" certification has been permitted to accommodate this practice. That is, the rotorcraft manufacturer shows compliance with the flotation time, trim, and emergency exit requirements while the purchaser or modifier shows compliance with the equipment provisions and egress requirements with the completed interior. This procedure requires close cooperation and coordination between the manufacturer, purchaser or modifier, and the FAA/AUTHORITY.
(i) The rotorcraft manufacturer may elect to establish a "token" interior for ditching certification. This interior may subsequently be modified by a supplemental Page D - 83
type certificate or a field approval. Compliance with the ditching requirements should be reviewed after any interior configuration changes and limitations changed where applicable.
(II) The Rotorcraft Flight Manual and supplements deserve special attention if a "segmented" certification procedure is pursued.
b. Procedures. The following guidance criteria has been derived from past certification policy and experience. Demonstration of compliance to other criteria may produce acceptable results if adequately justified by rational analysis. Model tests of the appropriate ditching configuration may be conducted to demonstrate satisfactory water entry and flotation and trim characteristics where satisfactory correlation between model testing and flight testing has been established. Model tests and other data from rotorcraft of similar configurations may be used to satisfy the ditching requirements where appropriate.
(1) Water entry.
Tests should be conducted to establish procedures and techniques to be used for water entry. These tests should include determination of optimum pitch attitude and forward velocity for ditching in a calm sea as well as entry procedures for the highest sea state to be demonstrated (e.g., the recommended part of the wave on which to land). Procedures for all-engines-operating, one-engine-inoperative, and all-engines-inoperative conditions should be established. However, only the procedures for the most critical condition (usually all engines inoperative) need to be verified by water entry tests.
(її) The ditching structural design consideration should be based on water impact with a rotor lift of not more than two-thirds of the maximum design weight acting through the center of gravity under the following conditions:
(A) For entry into a calm sea--
(1) The optimum pitch attitude as determined in AC 27.801(b)(1)(i) with consideration for pitch attitude variations that would reasonably be expected to occur in service;
(2) Forward speeds from zero up to the speed defining the knee of the height-velocity (HV) diagram;
(3) Vertical descent velocity of 5 feet per second; and
(4) Yaw attitudes up to 15°.
(B) For entry into the maximum demonstrated sea state-- Page D - 84
(1) The optimum pitch attitude and entry procedure as established in AC 27.801(b)(1)(I);
(2) The forward speed defined by the knee of the HV diagram reduced by the wind speed associated with each applicable sea state;
(3) Vertical descent velocity of 5 feet per second; and
(4) Yaw attitudes up to 15°.
(C) The float system attachment hardware should be shown to be structurally adequate to withstand water loads during water entry when both deflated and stowed and fully inflated (unless in-flight inflation is prohibited). Water entry conditions should correspond to those established in paragraphs AC 27.801(b)(1) (ii (A) and (B). The appropriate vertical loads and drag loads determined from water entry conditions (or as limited by flight manual procedures) should be addressed. The effects of the vertical loads and the drag loads may be considered separately for the analysis.
(D) Probable damage due to water impact to the airframe/hull should be considered during the water entry evaluations; i.e., failure of windows, doors, skins, panels, etc.
(E) The ditching maximum demonstrated sea state for water entry is the same or greater than the maximum demonstrated sea state for flotation and trim.
(2) Flotation Systems.
(i) Normally inflated. Fixed flotation systems intended for emergency ditching use only and not for amphibian or limited amphibian duty should be evaluated for:
(A) Structural integrity when subjected to:
(1) Air loads throughout the approved flight envelope with floats installed;
(2) Water loads during water entry; and
(3) Water loads after water entry at speeds likely to be experienced after water impact.
(B) Rotorcraft handling qualities throughout the approved flight envelope with floats installed.
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(ii) Normally deflated. Emergency flotation systems which are normally stowed in a deflated condition and inflated either in flight or after water contact during an emergency ditching should be evaluated for:
(A) Inflation. The float activation means may be fully automatic or manual with a means to verify primary actuation system integrity prior to each flight. If manually inflated, the float activation switch should be located on one of the primary flight controls. These activation means should be safeguarded against spontaneous or inadvertent actuation for all flight conditions.
(1) The inflation system design should minimize the probability of the floats not inflating properly or inflating asymmetrically. This may be accomplished by use of a single inflation agent container or multiple container system interconnected together. Redundant inflation activation systems will also normally be required. If the primary actuation system is electrical, a mechanical backup actuation system will usually provide the necessary reliability. A secondary electrical actuation system may also be acceptable if adequate electrical system independence and reliability can be documented.
(2) The inflation system should be safeguarded against spontaneous or inadvertent actuation for all flight conditions. It should be demonstrated that float inflation at any flight condition within the approved operating envelope will not result in a hazardous condition unless the safeguarding system is shown to be extremely reliable.
One safeguarding method that has been successfully used on previous certification programs is to provide a separate float system arming circuit which must be activated before inflation can be initiated.
(3) The maximum airspeed for intentional in-flight actuation of the float system and for flight with the floats inflated should be established as limitations in the RFM unless in-flight actuation is prohibited by the RFM.
(4) The inflation time from actuation to neutral buoyancy should be short enough to prevent the rotorcraft from becoming more than partially submerged assuming actuation upon water contact.
(5) A means should be provided for checking the pressure of the gas storage cylinders prior to takeoff. A table of acceptable gas cylinder pressure variation with ambient temperature and altitude (if applicable) should be provided.
(6) A means should be provided to minimize the possibility of overinflation of the float bags under any reasonably probable actuation conditions.
(Z) The ability of the floats to inflate without puncture when subjected to actual water pressures should be substantiated. A full-scale rotorcraft immersion demonstration in a calm body of water is one acceptable method of substantiation.
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Other methods of substantiation may be acceptable depending upon the particular design of the flotation system.
(B) Structural Integrity. The flotation bags should be evaluated for loads resulting from:
(1) Airloads during inflation and fully inflated for the most critical flight conditions and water loads with fully inflated floats during water impact for the water entry conditions established under paragraph AC 27.801(b)(1)(ii) for rotorcraft desiring float deployment before water entry; or
(2) Water loads during inflation after water entry.
(C) Handling Qualities. Rotorcraft handling qualities should be verified to comply with the applicable regulations throughout the approved operating envelopes for:
(1) The deflated and stowed condition;
(2) The fully inflated condition; and
(3) The in-flight inflation condition. For float systems which may be inflated in flight, rotorcraft controllability should be verified by test or analysis assuming the most critical float compartment fails to inflate.
(3) Flotation and Trim. The flotation and trim characteristics should be investigated for a range of sea states from zero to the maximum selected by the applicant and should be satisfactory in waves having height/length ratios of 1:12.5 for multiengine rotorcraft with Category A engine isolation and 1:10 for all other rotorcraft.
Model tests in a wave basin on a number of different rotorcraft types have indicated that an improvement in sea keeping, response of the rotorcraft to waves, performance of approximately one sea state can consistently be achieved by fitting float scoops. If the basic flotation system (without scoops) has demonstrated compliance with the minimum flotation and trim requirements, credit for float scoops to achieve stability in more severe water conditions may be allowed. However, the effect of scoops on improved sea keeping must be demonstrated during model testing.
(i) Flotation and trim characteristics should be demonstrated to be satisfactory to at least sea state 4 conditions.
(ii) Flotation tests should be investigated at the most critical rotorcraft loading condition.
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AC 27-1B, Chg 2 4/25/06 (III) Flotation time and trim requirements should be evaluated with a simulated, ruptured deflation of the most critical float compartment. Flotation characteristics should be satisfactory in this degraded mode to at least sea state 2 conditions.
(iv) A sea anchor or similar device should not be used when demonstrating compliance with the flotation and trim requirements but may be used to assist in the deployment of liferafts. If the basic flotation system has demonstrated compliance with the minimum flotation and trim requirements, credit for a sea anchor or similar device to achieve stability in more severe water conditions (sea state, etc.) may be allowed if the device can be automatically, remotely, or easily deployed by the minimum flightcrew.
(v) Probable rotorcraft door/window open or closed configurations and probable damage to the airframe/hull (i.e., failure of doors, windows, skin, etc.) should be considered when demonstrating compliance with the flotation and trim requirements.
(4) Float System Reliability. Reliability should be considered in the basic design to ensure approximately equal inflation of the floats to preclude excessive yaw, roll, or pitch in flight or in the water.
Maintenance procedures should not degrade the flotation system
(e.g., introducing contaminants which could affect normal operation, etc.).
(ii) The flotation system design should preclude inadvertent damage due to normal personnel traffic flow and excessive wear and tear. Protection covers should be evaluated for function and reliability.
(iii) Float design should provide a means to minimize the likelihood of damage or tear propagation between compartments. Single compartment float designs should be avoided.
(iv) Where practical, design of the flotation system should consider the likely effects of an uncontrolled water entry and locate system components away from the major effects of structural deformity.
(v) Visual identification of the helicopter following a ditching (and possible capsize) is made easier by the choice of material for the construction of the floats that has high visual conspicuity properties.
(5) Occupant Egress and Survival. The ability of the occupants to deploy liferafts, egress the rotorcraft, and board the liferafts should be evaluated. For configurations which are considered to have critical occupant egress capabilities due to liferaft locations and/or ditching emergency exit locations and floats proximity, an actual demonstration of egress may be required. When a demonstration is required, it may be conducted on a full-scale rotorcraft actually immersed in a calm body of water or using Page D - 88
any other rig/ground test facility shown to be representative. The demonstration should show that floats do not impede a satisfactory evacuation. Service experience has shown that it is possible for occupants to have escaped from the cabin but have not been able to board a liferaft and have had difficulties finding handholds to stay afloat and together. Where practical, handholds or lifelines should be provided. The normal attitude of the rotorcraft and the possibility of a capsize should be considered when locating the handholds or lifelines.
(6) Rotorcraft Flight Manual. The Rotorcraft Flight Manual is an important element in the approval cycle of the rotorcraft for ditching. The material related to ditching may be presented in the form of a supplement or a revision to the basic manual. This material should include:
(i) The information pertinent to the limitations applicable to the ditching approval should include the range of sea state conditions that has been demonstrated for water entry and flotation stability. If the ditching approval is obtained in a segmented fashion (i.e., one applicant performing the aircraft equipment installation and operations portion and another designing and substantiating the liferaft/lifevest and ditching safety equipment installations and deployment facilities), the RFM limitations should state "Not Approved for Ditching" until all segments are completed. The requirements for a complete ditching approval not yet completed should be identified in the "Limitations" section.
(ii) Procedures and limitations for flotation device inflation.
(III) Recommended rotorcraft water entry attitude, speed, and wave position.
(iv) Procedures for use of emergency ditching equipment.
(v) Procedures for ditching egress and raft entry.
(vi) Information stating the flotation system has been certificated for Ditching (as opposed to Emergency Flotation) to facilitate compliance with operational requirements.
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AC 27.801-1
SEA STATE CODE (WORLD METEOROLOGICAL ORGANIZATION) Sea State Significant Wave Height Wind Speed Code Description of Sea Meters Feet Knots Calm (Glassy) 0-3 Calm (Rippled) O to 0.1 O to 1/3 4-6 2 Smooth (Wavelets) 0.1 to 0.5 1/3 to 1 2/3 7-10 Slight 0.5 to 1.25 1 2/3 to 4 11-16 Moderate 1.25 to 2.5 4 to 8 17-21 5 Rough 2.5 to 4 8 to 13 22-27 6 Very Rough 4 to 6 13 to 20 28-47 7 High 6 to 9 20 to 30 48-55 8 Very High 9 to 14 30 to 45 56-63 9 Phenomenal Over 14 Over 45 64-118 NOTES: (1) The Significant Wave Height is defined as the average value of the height (vertical distance between trough and crest) of the largest one-third of the waves present.
Maximum Wave Height is usually taken to be 1.6 x Significant Wave Height; e.g., Significant Wave Height or 6 meters gives Maximum Wave Height of 9.6 meters.
(3) Winds speeds were obtained from Appendix R of the "American Practical Navigator" by Nathaniel Bowditch, LL.D.; Published by the U.S. Naval Oceanographic Office, 1966.
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