the ground. During tethered hover tests, the rotorcraft should be at light gross weight.
The rotorcraft will be stabilized at a fixed power setting and rotor speed at the appropriate skid or wheel height. Once the required data are obtained, power should be varied from the minimum to the maximum allowed at various rotor RPM. This technique will produce a large Ct/Cp spread. The load cell reading is recorded for each stabilized point. The total thrust the rotor produces is the rotorcraft’s gross weight, weight of the cables and load cell plus cable tension. Care must be taken that the cable tension does not exceed the cargo hook limit or load capacity of the tie-down. For some rotorcraft, it may be necessary to ballast the rotorcraft to a heavy weight in order to record high power hover data.
(2) The pilot maintains the rotorcraft in position so that the cable and load cell are perpendicular to the ground. To insure the cable is vertical, two outside observers, one forward of the rotorcraft and one to one side, can be used. Either hand signals or radio can be used to direct the pilot. The observers should be provided with protective equipment. This can also be accomplished by attaching two accelerometers to the load cell which sense movement along the longitudinal and lateral axes. Any displacement of the load cell will be reflected on instrumentation in the cockpit and by reference to this instrumentation, the rotorcraft can be maintained in the correct position. Accurate load cell values may also be obtained by measuring cable angles and, through geometry, determining a corrected load cell value. Increased caution should be utilized as tethered hover heights are decreased because the rotorcraft may become more difficult to control precisely. The tethered hover technique is especially useful for OGE hover performance data because the rotorcraft’s internal weight is low and the cable and load cell can be jettisoned in the event of an engine failure or other emergency.
(3) To obtain consistent data, the wind velocity should be 3 knots or less. Large rotorcraft with high downwash velocities may tolerate higher wind velocities. The parameters usually recorded at each stabilized condition are:
(i) Engine and transmission torque.
(ii) Rotor speed.
(iii) Ambient and engine temperatures, such as measured gas temperature (MGT).
(iv) Pressure altitude.
(v) Fuel used (or remaining).
(vi) Load cell reading.
(vii) Generator(s) load.
(viii) Wind speed and direction.
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AC 29-2C, Chg 4 5/1/2014
(ix) Hover height.
As a technique, it is recommended the rotorcraft be loaded to a center of gravity (CG) near the hook to minimize fuselage angle changes with varying powers. All tethered hover data should be verified by a limited spot-check using the free flight technique.
The free flight technique in paragraph b.(4) below will determine if any problems, such as load cell malfunctions, have occurred. The free flight hover data must fall within the allowable scatter of the tethered data.
(4) If there are no provisions or equipment to conduct tethered hover tests, the free flight technique is also a valid method. The disadvantage of this technique as the primary source of data acquisition is that it is very time consuming. In addition a certain element of safety is lost OGE in the event of emergency. The rotorcraft must be reballasted to different weights to allow the maximum Ct/Cp spread. When using the free flight technique, either as a primary data source or to substantiate the tethered technique, the same considerations for wind, recorded parameters, etc., as used in the tethered technique apply. Free flight hover tests should be conducted at CG extremes to verify any CG effects. If the rotorcraft has any stability augmentation system, which may influence hover performance, it must be accounted for.
(5) Comprehensive hover performance tests are typically conducted at low, intermediate (approximately 7000 feet HD), and high altitude test sites with prepared landing surfaces, in conjunction with takeoff, landing, controllability, and maneuverability testing. Alternatively, a predicted hover performance model developed for high altitude may be used if verified by limited flight testing. The extrapolation guidelines in section
29.45.b.(2) of this AC are still applicable. These higher altitude hover tests could typically be conducted in conjunction with the limited controllability tests. If the applicant is able to demonstrate to the approving airworthiness authority a method to provide a reliable hover reference, it is acceptable to conduct OGE tests without ground reference.
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AC 29.51. § 29.51 TAKEOFF DATA - GENERAL.
a. Explanation. Section 29.51 details the conditions under which takeoff performance data can be obtained and presented in the FAA/AUTHORITY approved flight manual. The flight manual must also contain the technique(s) to be used to obtain the published flight manual takeoff performance. Technique should not be confused with exceptional pilot skill and/or alertness as mentioned in § 29.51. Rotorcraft are different from one another and due to this, different pilot techniques are sometimes required to achieve the safest and most optimum takeoff performance. The recommended technique that is published in the flight manual and used to achieve the performance must be determined to be one that the operational pilot can duplicate using the minimum amount of type design cockpit instrumentation and the minimum crew.
b. Background.
(1) Certain special takeoff techniques are necessary when a rotorcraft is unable to takeoff vertically because of altitude, weight, power effects, or operational limitations.
The recommended technique used to take off under such conditions is to accelerate the rotorcraft in-ground-effect (IGE) to a predetermined airspeed prior to climbout. Takeoff tests are performed to determine the best repeatable technique(s) for a particular rotorcraft over the range of weight, altitude, and temperature for which certification is requested.
(2) The primary factor which determines the rotorcraft’s takeoff performance is the amount of excess power available. Excess power available is the difference between the power required to hover at the reference height above the ground and the takeoff power available from a minimum installed specification engine. Utilizing the total power available to execute a takeoff may not be operationally feasible due to such items as HV constraints. In such situations, hover power required plus some power increment may be the maximum that can be used and the resulting performance determined accordingly.
(3) Landing gear height above the ground should not be greater than that demonstrated satisfactorily for HV, rejected takeoff, and that height for which IGE hover performance data is presented in the RFM, or less than that height below which ground contact may occur when accomplishing takeoff procedures. For rotorcraft fitted with wheels, a running takeoff procedure may be accepted. The hover reference height is established as the minimum landing gear height above the takeoff surface, from which a takeoff can be accomplished consistently in zero wind without contacting the runway.
Category B takeoff must be accomplished with power fixed at the power required to hover at the reference height (not greater than the height for which IGE performance data is presented).
c. Procedure. There are different techniques which may be used in order to determine which method is best for a particular rotorcraft. The most commonly accepted method is the hover and level acceleration technique. In this technique, the Page B – 29
AC 29-2C, Chg 4 5/1/2014 rotorcraft is stabilized in a hover at the reference height. From the stabilized hover, the rotorcraft is accelerated to the climbout airspeed using the predetermined takeoff power.
When the desired climbout airspeed is achieved, the rotorcraft is rotated and the climbout is accomplished at the schedule airspeed(s) and constant rotor RPM. Power adjustments may be accomplished to maintain targeted power except where procedure requires high workload outside cockpit (i.e., that portion of takeoff where horizontal acceleration close to the ground has pilot scan outside the cockpit and adjustment of engine torque or temperature would require an undue increase in workload).
AC 29.51A. § 29.51 (Amendment 29-39) TAKEOFF DATA - GENERAL.
a. Explanation. Amendment 39 added takeoff requirements in new §§ 29.55, 29.60,
29.61 and 29.62.
b. Procedures. The guidance material presented in paragraph AC 29.51 continues to apply.
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AC 29.53. § 29.53 TAKEOFF: CATEGORY A.
a. Explanation.
(1) A Category A takeoff typically begins with an acceleration and/or climb from a hover to a critical decision point. The rule requires that the critical decision point (CDP) be defined for the pilot in terms of an indicated altitude and airspeed combination. However, other parameters to define the CDP have been accepted by the FAA/AUTHORITY on an equivalent safety basis. A regulatory project has been established to change the rule permitting other parameters to be used for CDP definition.
(2) The requirement to define CDP as a combination of both airspeed and height above the takeoff surface is based on a minimum required total energy concept.
A specific minimum combination of kinetic energy (airspeed) and potential energy (height) must be attained at the CDP to be assured that a continued takeoff can be accomplished following the complete failure of one engine. In § 29.53(b), CDP is required to be “…a combination of height and speed selected by the applicant…” Any other method proposed to define CDP must provide the same level of safety as would be obtained using an airspeed-height combination. When using “time,” “height,” or “airspeed” only as alternative methods of identifying the CDP, they must be combined with a precisely defined takeoff path and crew procedure in order to provide the required equivalent level of safety. In addition, it must be demonstrated that the pilot technique used during the takeoff sequence is easily repeatable and consistently produces the required energy (i.e., airspeed and altitude combination) when the CDP “time,” “height,” or “airspeed” is attained. This condition should be verified during the flight test program.
(3) If an engine fails at the CDP or at any point in the takeoff profile prior to attaining CDP, the rotorcraft must be able to land safely within the established rejected takeoff distance. Flight testing to determine the Category A rejected takeoff distance is very similar to height-velocity testing and should be approached with caution. The initial Category A takeoff profiles should be outside of the Category B height-velocity envelope. Previous programs have shown the low speed point immediately after application of power to be particularly critical.
(4) If an engine fails at the CDP or at any subsequent point in the Category A takeoff profile, a continued safe climb-out capability is assured. The continued takeoff for conventional Category A runway profiles is designed to allow acquisition of the takeoff safety speed (VTOSS), at a minimum of 35 feet above the takeoff surface and a positive rate of climb. During the continued takeoff profile, the pilot is assumed to be flying the rotorcraft via the primary flight controls (cyclic stick, collective, and directional pedals). Manipulation of the throttle controls or beep switches may be permitted as long as such manipulation can be accomplished readily by the pilot flying the rotorcraft without removing his hands from the cyclic and collective flight controls. These manipulations of engine controls should not make major adjustments in power, and Page B - 31
should not occur before attaining VTOSS. In no case should this be less than 3 seconds after the critical engine is made inoperative.
(5) Both the rejected takeoff distance and the continued takeoff distance must be determined. Although 29.59(c) suggests a balanced field length requirement, this was not intended. Both rejected and continued takeoff distance should be included in the RFM performance with information stating that the longer distance determines the length of the required takeoff surface. Operations approvals can then determine the required takeoff surface (including stopways and clearways) appropriate for the specific operation.
(6) A typical Category A takeoff profile, assuming an engine failure at the CDP, is shown in figure AC 29.53-1.
b. Procedures.
None.
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HEIGHT ABOVE (CONFIGURATION AN IF APPROPRIATE VD POWER CHAN GROUND (FEET)
CDP VTOSS 35 (RTO) STOP
- ALL ENGINES OPERATING DEITRANSITION SEGMENT - TAKEOFF CLIMB SEGMENT
TAKEOFF SEGMENT
RTO SEGMENT
DEMONSTRATED SAFE OEILANDINGS
HORIZONTAL DISTANCE FIGURE AC 29.53-1 TAKEOFF PERFORMANCE CATEGORY A Page B - 33
AC 29.53A. § 29.53 (Amendment 29-39) TAKEOFF: CATEGORY A.
a. Explanation. Amendment 29- 39 separated in the text, the Category A takeoff requirement from the definition of a decision point. Category A takeoff performance must be scheduled so that:
(1) If an engine failure is recognized at the Takeoff Decision Point (TDP) or at any point in the takeoff profile prior to attaining TDP, the rotorcraft must be able to land safely within the established rejected takeoff distance. Flight testing to determine the Category A rejected takeoff distance is very similar to height-velocity testing and should be approached with caution. The initial Category A takeoff profiles should be outside of the avoid area of the Category B height-velocity envelope. Previous programs have shown the low speed point immediately after application of power to be particularly critical.
(2) If an engine failure is recognized at the TDP or at any subsequent point in the Category A takeoff profile, a continued safe climb-out capability must be assured.
The continued takeoff for conventional Category A runway profiles is designed to allow acquisition of the takeoff safety speed (VTOSS) at a minimum of 35 feet above the takeoff surface and a positive rate of climb.
(3) Both the rejected takeoff distance and the continued takeoff distance should be determined. A balanced field length is not required by the regulation. Both rejected and continued takeoff distance should be included in the RFM performance section.
Operations approvals can then determine the required takeoff surface (including stopways and clearways) appropriate for the specific operation.
(4) A typical Category A takeoff profile, assuming an engine failure prior to the TDP, is shown in figure AC 29.53A-1.
b. Procedures. None.
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Vv ≥ 150 fpm 1000 ft.
(29.67a.2) 1000 ft.
2nd Segment Height Above Ground (ft) Vy LEVEL ACCEL TO Vy 200 ft. H-V AVOID (29.87) (29.67 a.1) V, ≥ 100 fpm i Segment 200 ft.
шини EFPA TDP (29.59) VTOSS 35 ft. 35 ft.
15 ft. TOl 15 ft.
O ft.
Rejected T.O. Dist (29.62) Horizontal Distance T.O. Dist (29.61) FIGURE AC 29.53A-1 TAKEOFF PERFORMANCE CATEGORY A Page B - 35
AC 29.55. § 29.55 (Amendment 29-39) TAKEOFF DECISION POINT:
CATEGORY A.
a. Explanation.
(1) Amendment 29-39 added a new § 29.55 to redefine the TDP (previously called the CDP) and contained in § 29.53; it further removed the requirement to identify the TDP by height and airspeed, since height alone or other factors may be more appropriate. A Category A takeoff typically begins with an acceleration and/or climb from a hover to TDP. The rule requires that the TDP be defined for the pilot in terms of no more than two parameters such as an indicated height and airspeed combination.
(2) The definition of the TDP is based on a minimum required total energy concept. A specific minimum combination of kinetic energy (airspeed) and potential energy (height) should be attained at the TDP to ensure that a continued takeoff can be accomplished following the complete failure of one engine. In § 29.55(b), TDP is required to be defined by no more than two parameters. When using a single parameter such as time, height, or airspeed as a method of identifying the TDP, the identification must be combined with a precisely defined takeoff path and crew procedure to provide the required equivalent level of safety. In addition, it should be demonstrated that the pilot technique used during the takeoff sequence is easily repeatable and consistently produces the required energy (i.e., airspeed and height combination) when the TDP time, height, or airspeed is attained. This condition should be verified during the flight test program.
b. Procedures. None.
AC 29.59. § 29.59 (Amendment 29-24) TAKEOFF PATH: CATEGORY A.
a. Explanation. The Category A concept limits the rotorcraft takeoff weight such that if an engine failure occurs at or before the CDP, a safe landing can be made or if the engine fails at or after the CDP, the takeoff can be continued. The purpose of these tests is to define the CDP, evaluate the necessary pilot techniques, and determine the required takeoff area for either alternative. The condition of equal distances for either stopping or continuing the takeoff is called a “balanced” field length. The combination of altitude and speed at the CDP which produces a balanced field length is not required for certification. This section deals with the Category A takeoff and rejected takeoff profiles. The profiles necessarily involve consideration of an average pilot skill level as well as a sequence in which it is assumed various configuration adjustments are made to the rotorcraft.
(1) Takeoff. The Category A takeoff path begins with an all -engines-operating acceleration segment to the CDP and continues with a one-engine-inoperative acceleration to takeoff safety speed (VTOSS). (See Conventional Takeoff Profile, figure AC 29.53-1, paragraph AC 29.53.) CDP is a “go/no -go” condition which is analogous to V1 speed in transport airplanes. Prior to CDP the pilot is “stop” oriented, Page B - 36
and when an engine fails in this portion of the takeoff, he will abort because he has not yet achieved sufficient energy to assure continued flight. At the CDP the pilot becomes “go” oriented and when an engine fails at or beyond this point he will continue the takeoff because he no longer has sufficient surface area to abort the takeoff. The takeoff flight path and the CDP must be defined such that a safe landing can be made from any point up to the CDP. This profile may differ significantly from the takeoff flight path developed for Category B weights. The CDP is the last point in the takeoff profile at which a rejected takeoff capability within the scheduled takeoff surface distance is assured. If an engine failure does not occur, the pilot continues the climb and accelerates past the CDP to the recommended climb speed.
(2) Rejected Takeoff. The rejected takeoff profile begins with an all engine acceleration segment to the CDP and ends when the rotorcraft is brought to a complete stop on the designated takeoff surface. The critical engine is made inoperative at the CDP and the landing must be made with the remaining engine(s) operating within approved limits. The rejected takeoff distance is normally measured at a given reference point on the rotorcraft from the start of the takeoff to the same reference point after the rotorcraft has come to a complete stop. This distance should be increased by the rotorcraft length (including main and tail rotor tip paths).
(3) Takeoff Climbout Path.
(i) The “OEI transition segment” is defined as the segment from CDP where the engine becomes inoperative to VTOSS. It is assumed that the maximum approved OEI power is used until the allowable time duration for that power is exhausted. It must be possible for the crew to fly the rotorcraft to V TOSS and attain an altitude of 35 feet and then climb to 100 feet above the takeoff surface by flying the rotorcraft solely by the primary flight controls (including collective). The landing gear may be retracted after attaining a height of 35 feet above the takeoff surface, a speed of VTOSS, and a positive rate of climb. Flight manual procedures may recommend adjustment of auxiliary controls to improve OEI performance. However, compliance with the performance requirements of § 29.67(a)(1) should not be based on use of secondary engine controls such as beepers, etc. Manipulation of the throttle controls or beep switches may be permitted for compliance with the performance requirements of § 29.67(a)(2) as long as such manipulation can be accomplished readily by the pilot flying the rotorcraft without removing his hands from the cyclic and collective flight controls. These manipulations of secondary engine controls should not make major adjustments in the power, and should not occur before attaining VTOSS. There should be a minimum delay of 3 seconds after the critical engine is made inoperative before adjustment of secondary engine controls is allowed during the takeoff path determination. The failure of one engine cannot affect continued safe operation of the remaining engines or require any immediate action by the crew per § 29.903(b). If a 2 ½-minute power rating is used, it should be possible to complete the Category A takeoff profile (assuming an engine failure at CDP), accelerate to VTOSS, attain 35 feet above the surface, and complete landing gear retraction prior to exhausting the 2 ½-minute time limit.
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(ii) The takeoff safety speed, VTOSS, is a speed at which 100 FPM rate of climb is assured under conditions defined in § 29.67(a)(1). The takeoff distance is the distance from initial hover to the point at which VTOSS and 35 feet in a climbing posture are attained.
(4) Continued Climbout Path. Continued acceleration and climb capability from 100 feet above the takeoff surface is assured by the 100 FPM VTOSS climb requirement of § 29.67(a)(1) and the 150 FPM requirement of § 29.67(a)(2), normally demonstrated at VY . It should be shown that the rotorcraft can be accelerated from V TOSS to VY in a continuous maneuver without losing altitude, including any configurative change (landing gear retraction, etc.).
b. Procedures.
(1) Instrumentation. A photo theodolite, grid camera, or other position measuring equipment is required together with a ground station to measure wind, OAT, humidity (if applicable), and a two-way communication system to coordinate activities with the aircraft. A crash recovery team with support of a fire engine is highly desirable.
Aircraft instrumentation should record with a time scale: engine parameters (speed, temperature, and power), rotor speed, flight parameters (airspeed, altitude, and normal acceleration as a minimum), flight control positions, power lever position, and landing gear loads. Additionally, a method should be devised to allow correlation of the aircraft instrumentation data with the space position data to accurately determine the length of the various takeoff segments.
(2) Establishing the Critical Decision Point (CDP).
(i) The CDP should be definable with the minimum crew using standard cockpit instrumentation. If a radar altimeter is used, it should be included in the minimum equipment list. If barometric altitude is used to define CDP, the operating conditions at which the altimeter is set should be defined. This is normally done on the ground with the minimum collective pitch. If the wind influences the altimeter reading, the correct relative wind information should be provided. Unless the rotorcraft is capable of hovering with one engine inoperative at the desired Category A weight, the CDP becomes largely a function of the surface area required for takeoff. If takeoff conditions scheduled include considerable surface area (on the order of 2,000 feet), the CDP airspeed may be a high value near VY. This will allow a higher takeoff weight and demonstrate compliance with the VTOSS climb requirement of § 29.67(a)(1). In this case, the requirements of § 29.67(a)(2) usually become limiting. If required surface area is a small value, CDP will necessarily be some lower airspeed value to allow for an aborted takeoff on the available surface. Weight may need to be reduced at lower values of CDP airspeed (significantly below VY) to allow compliance with the climb requirement of § 29.67(a)(1). Compliance with climb requirements can be substantiated initially by testing at a safe altitude above the ground. When OEI climb conditions are verified for Page B - 38