337A. § 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 337 of this AC 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.
338. § 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.
(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:
(i) 1:12.5 for multiengine rotorcraft with Category A engine isolation (reference Paragraph 780).
(ii) 1:10 for all other rotorcraft.
NOTE: The source of the sea state definition is the World Meteorological Organization (WMO) Table. (See Table 338-1.)
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(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.
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.
(її) The rotorcraft manufacturer may elect to establish a "token" interior for ditching certification. This interior may subsequently be modified by a supplemental type certificate or a field approval. Compliance with the ditching requirements should be reviewed after any interior configuration changes and limitations changed where applicable.
(iii) The Rotorcraft Flight Manual and supplements deserve special attention if a "segmented" certification procedure is pursued.
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АС 27-1А 7/30/97
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 satisty 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 338(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;
(2) Vertical descent velocity of 5 feet per second; and
(4) Yaw attitudes up to 15°.
(B) For entry into the maximum demonstrated sea state--
(1) The optimum pitch attitude and entry procedure as established in 338(b)(1)(1);
(2) The forward speed defined by the knee of the HV diagram reduced by the wind speed associated with each applicable sea state;
426 Par 338
(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 338(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.
(2) Flotation Systems.
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.
(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 primary actuation system to verify 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.
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(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.
(L) 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. 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 338(b)(1)(ii) for rotorcraft desiring float deployment before water entry; or 428 Par 338
(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 a 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.
Flotation and trim characteristics should be demonstrated to be satisfactory to at least sea state 4 conditions.
(її) Flotation tests should be investigated at the most critical rotorcraft loading condition.
(ili) 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.
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(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.
(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 any other rig/ground test facility shown to be representative. The demonstration should show that floats do not impede a satisfactory evacuation.
(6) Botorcraft 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:
The information pertinent to the limitations applicable to the ditching approval. If the ditching approval is obtained in a segmented fashion (l.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.
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TABLE 338-1
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 3 Slight 0.5 to 1.25 1 2/3 to 4 11-16
• 4 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 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.
(2) 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 Navigatori by Nathaniel Bowditch, LL.D.; Published by the U.S. Naval Oceanographic Office, 1966.
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339. RESERVED.
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340. § 27.807 (Amendment 27-21) EMERGENCY EXITS.
a. Explanation. The specified emergency exits are as follows:
(1) Quantity, size, and location.
(1) For typical operations.
Passenger Seating Capacity Main Door (MD) Side Side Opposite Main Door 1 through 15 MD (1) 19- by 26-inch ellipse More than 15 MD + additional (1) 19- by 26-inch ellipse + exit(s) additional exit(s) For overwater operations (if ditching certification is requested), one 19- by 26-inch elliptical exit on each side of the fuselage above the waterline.
(i1) Section 27.807(a) was revised by Amendment 27-21 on November 6, 1984, to remove any reference to the seating capacity in excess of 15 seats. For further information, see Amendment 29-21 which, in part, amended § 29.1 on January 31, 1983.
(2) In addition to quantity and size of exits, the rule specifies the following:
The 19- by 26-inch ellipse portion of the exit is to be unobstructed.
(її) The exits are to be readily accessible.
(i) The exits must have a simple and obvious method of opening.
(iv) The exits must be readily located and operated in darkness.
(v) The exits must be protected from jamming by fuselage deformation.
b. Procedures.
(1) The quantity and minimum size of exits will be as specified.
(2) Access to the exits will be provided by aisles, break-over seatbacks, or other features as appropriate. If access is questionable, a demonstration shall be conducted to assess the means of access.
(3) The location and operation of the exits should be evaluated in total darkness.
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(4) Protection from jamming is normally provided by clearances between the fuselage exit frame and the exit or by exit designs which are basically insensitive to fuselage deformation. NASTRAN or similar analysis methods have been used in the past to obtain the effects of fuselage deformation on exit clearances during minor crash landings.
340A. § 27.807 (Amendment 27-26) EMERGENCY EXITS.
a. Explanation. Amendment 27-26 added § 27.807(d)(3) which requires proof that all rotorcraft ditching configuration exits will also be free of interference from emergency flotation devices, whether stowed or deployed (inflated).
b. Procedures. All of the policy material pertaining to this section remains in effect with the following additions:
(1) Test, demonstration, compliance inspection, or analysis is required to show the "ditching" exits are free from interference from stowed/deployed emergency flotation devices. In the event an analysis is insufficient or a given design is questionable, a demonstrating may be required. The demonstration would consist, as a minimum, of an accurate, full-size replica (or representation) of the rotorcraft and of the flotation devices both before, during, an after their deployment.
(2) The type inspection authorization may be used to perform a detailed compliance evaluation utilizing a full-scale rotorcraft in calm water.
(3) Designs may be accepted "by compliance visual inspection" if location of exit and flotation devices relative to each other ensure that interference is impossible.
In this case, a demonstration is unnecessary.
341.-344. RESERVED.
434 (thru 438) Par 340
345. § 27.831 VENTILATION.
a. Explanation.
(1) This rule specifies minimum ventilation requirements for each passenger and crew compartment. The passenger and crew compartments are required to be free from harmful or hazardous concentration of gases or vapors, and specifically for carbon monoxide, its concentration may not exceed 1 part in 20,000 parts of air during forward flight or hovering in still air.
(2) Failure conditions must also be considered when evaluating the ventilation system, and § 27.1309 is used to cover these aspects. Malfunctions concerning the ventilation system are covered here to make the discussion complete in one paragraph.
(3) This system becomes more significant when engine bleed air is used for conditioning of the passenger and crew compartment's air. Certain data are necessary in order to properly analyze the bleed air provided under normal and malfunction conditions. The airframe manufacturer can normally look to the engine manufacturer for a specification of the maximum amount of air that can be extracted and the temperature of the extracted air. The engine manufacturer also normally provides a failure analysis that identifies ways the bleed air can be contaminated and the associated oil flow rates under each failure condition. The oil manufacturers are in a position to provide information regarding breakdown of the oil under different temperature conditions and the impact of that breakdown on the quality of the air being provided to the passenger and crew compartments.
b. Procedures.
(1) The passenger and crew compartments should be monitored under normal operating conditions for the presence of carbon monoxide. A carbon monoxide test kit is normally used for this evaluation. Air is monitored around crew stations, and outlets and different combinations of windows closed/open, heat off/on, air-conditioner off/on, etc., are checked to ensure all conditions are evaluated.
(2) When engine bleed air is used to condition the passenger and crew compartment's air, it should be initially substantiated that under normal operation, the amount of air being extracted does not exceed the limit established by the engine manufacturer. To accomplish this, determine the flight condition that will give the maximum bleed air flow through the flow limiter (venturi). The flow calculations should use this maximum flow condition and should also be made using the maximum tolerance diameter of the venturi throat.
(3) The engine bleed air should also be evaluated under malfunction conditions to determine a worst-case air contamination condition. (A typical worst-case malfunction is for an oil seal to fail in the engine that allows the engine oil supply to be Par 345 439