ISSUE PAPER PROJECT: Generic Airplane Company ITEM:
ANM-110-XXX STAGE:
REG.REF.: § 1.2 (Abbreviations and symbols); All FAR 25 sections, except structural, dealing with stall speeds and related factors; and FAR 36 Noise standards (Appendix C) DATE:
Generic IP Revised 11/14/97
NATIONAL POLICY REF.: NONE ISSUE STATUS: OPEN SUBJECT: Use of 1-g Stall Speeds Instead of Minimum Speed in the Stall as a Basis for Determining Compliance BRANCH ACTION: -160x
COMPLIANCE TARGET: Pre-TC
EQUIVALENT SAFETY FINDING STATEMENT OF ISSUE:
Generic may elect to use 1-g stall speeds, rather than “traditional” V SMIN stall speeds, as the reference datum for regulatory compliance. Use of 1-g stall speeds as the performance basis requires changes to related abbreviations and symbols in FAR 1, and speeds based on multiples of stall speed presented in Subparts B, D, E, and F of FAR 25, and FAR 36. Speed factors in Subpart C of FAR 25 remain unchanged, since they have been applied historically to 1-g stall speeds, not V SMIN stall speeds.
If Generic elects to use the traditional V SMIN to define stall speed, the FAA will require the ratio of V SMIN/VS1-G to be greater than or equal to 0.94 to ensure that application of the subsequent operating speed margins will provide adequate protection from stall. With this additional limitation on allowable V SMIN, all associated operating speed margins will be calculated based on current FAR 25 requirements (e.g., V 2MIN = 1.2VSMIN).
BACKGROUND:
An equivalent safety finding for the use of 1 -g stall speeds, instead of the minimum speeds obtained in the st alling maneuver, as the basis for showing compliance with certain FAR 25 performance, and FAR 36 noise requirements, was established for several past type certification projects. Pilot objectivity on stall identification has become a key factor in decisions on flying technique, especially where deterrent buffet or excessively low load factors are developed during stalls to V SMIN. To avoid these problems, and to become consistent with recent certification practice, the application of 1-g stall speed criteria is being expanded to include most areas of the transport-related regulations that use stall speed as a factor.
The 1-g stall requirements were derived to provide a more realistic and consistent basis for the definition of stall speed as the minimum speed at which wing lift alone can support the weight of the airplane in level flight. Service history has not indicated a safety related deficiency in existing operating speeds that typically have their minimum
allowable values defined as a multiple of the V SMIN stall speed. Consequently, the 1-g stall Issue Papers have applied reduced operating speed factors for determining the minimum operating speeds in order to compensate for the 1-g stall speeds being higher than V SMIN speeds. The net result was little or no change in operating speeds for airplanes with aerodynamic stall, thus leading to a finding of equivalent safety.
FAA POSITION:
The following constitutes the FAA Equivalent Safety Finding for the Generic Model XYZ airplane:
CFR 14 Reference Equivalent Interpretations for Generic Model XYZ Part 1 (Definitions and abbreviations)
1.1 Add the following new definitions:
“Final takeoff speed means the speed of the airplane that exists at the end of the takeoff path in the en route configuration with one engine inoperative.”
“Reference landing speed means the speed of the airplane, in a specified landing configuration, at the point where it descends through the landing screen height in the determination of the landing distance for manual landings.”
1.2 Add the following new abbreviations:
“VFTO means final takeoff speed.”
“VREF means reference landing speed.”
“VSR means reference stall speed.”
“VSR0 means reference stall speed in the landing configuration.”
“VSR1 means reference stall speed in a specific configuration.”
“VSW means speed at which onset of natural or artificial stall warning occurs.”
Part 25 (Airworthiness Standards:
Transport Category Airplanes)
25.103(a) Change to read: “The reference stall speed , VSR, is a calibrated airspeed defined by the applicant. V SR may not be less than a 1- g stall speed. VSR is expressed as:
V V n SR CLMAX zw ≥ where___ VCLMAX = Calibrated airspeed obtained when the load factor-corrected lift coefficient ( n W qS zw ) is first a maximum during the maneuver prescribed in paragraph (c) of this section. In addition, when the maneuver is limited by a device that abruptly pushes the nose down at a selected angle of
attack (e.g., a stick pusher), VCLMAX may not be less than the speed existing at the instant the device operates;
nZW = Load factor normal to the flight path at VCLMAX;
W = Airplane gross weight;
S = Aerodynamic reference wing area; and q = Dynamic pressure.
VCLMAX is determined with:”
25.103(a)(1) Change to read: “Engines idling, or, if that resultant thrust causes an appreciable decrease in stall speed, not more than zero thrust at the stall speed;”
25.103(a)(2) Change to read: “Propeller pitch controls (if applicable) in the takeoff position;”
25.103(a)(3) Insert a new paragraph that reads: “The airplane in other respects (such as flaps and landing gear) in the condition existing in the test or performance standard in which V SR is being used;”
25.103(a)(4) Renumbering of the old § 25.103(a)( 3) and change “V S” to “VSR.”
25.103(a)(5) Change to read: “The center of gravity position that results in the highest value of reference stall speed; and”
25.103(a)(6) Insert a new paragraph that reads: “The airplane trimmed for straight flight at a speed selected by the applicant, but not less than 1.13 VSR and not greater than 1.30 V SR.”
25.103(b) Change to read: “Starting from the stabilized trim condition, apply elevator control to decelerate the airplane so that the speed reduction does not exceed one knot per second.”
25.103(b)(1) Remove this paragraph.
25.103(b)(2) Remove this paragraph.
25.103(c) Insert a new paragraph that reads: “In addition to the requirements of paragraph (a) of this section, when a device that abruptly pushes the nose down at a selected angle of attack (e.g., a stick pusher) is installed, the reference stall speed, V SR, may not be less than 2 knots or 2 percent, whichever is greater, above the speed at which the device operates.”
25.107(b)(1) Change “1.2 VS” to “1.13 VSR.”
25.107(b)(2) Change “1.15 VS” to “1.08 VSR.”
25.107(c)(3) Insert a new paragraph that reads: “A speed that provides the maneuvering capability specified in § 25.143(g).”
25.107(g) Insert a new paragraph that reads: “V FTO, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by § 25.121(c), but may not be less than--
(1) 1.18 VSR; and
(2) A speed that provides the maneuvering capability specified in § 25.143(g).”
NOTE: Unless AOA protection system (stall warning and stall identification) production tolerances are acceptably small, so as to produce insignificant changes in performance determinations, the flight test settings for stall warning and stall identification should be set at the low AOA tolerance limit; high AOA tolerance limits should be used for characteristics evaluations.
25.111(a) Replace “a speed is reached at which compliance with §
25.121(c) is shown” with “V FTO is reached.”
25.119(b) Change to rea d: “A climb speed of not more than V REF.”
25.121(c) Change to read: “...for four engine airplanes, at V FTO and with – ”
25.121(d) Change to read: “In a configuration corresponding to the normal all-engines-operating procedure in which V SR for this configuration does not exceed 110 percent of the V SR for the related all-engines-operating landing configuration, the steady gradient of climb may not be less than 2.1 percent for twoengine airplanes, 2.4 percent for three-engine airplanes, and 2.7 percent for four-engine airplanes, with –”
25.121(d)(3) Change to read: “...but not more than 1.4 V SR; and”
25.121(d)(4) Add new paragraph as follows: “Landing gear retracted.”
25.125(a)(2) Change to read: “A stabilized approach, with a calibrated airspeed of not less than V REF, must be maintained down to the 50 foot height. VREF may not be less than ___
(i) 1.23 VSR0; and
(ii) VMCL established under § 25.149(f); and
(iii) A speed that provides the maneuvering capability specified in § 25.143(g).”
25.143(g) Insert a n ew paragraph that reads: “The maneuvering capabilities in a constant speed coordinated turn at forward center of gravity, as specified in the following table, must be free of stall warning or other characteristics that might interfere with normal maneuvering:
CONFIG-
URATION SPEED
MANEUVERING
BANK ANGLE IN A
COORDINATED TURN
THRUST/POWER
SETTING TAKEOFF V2 30° ASYMMETRICWAT-LIMITED.1 TAKEOFF V2 + XX 2 40° ALL-ENGINES-OPERATING CLIMB.3 ENROUTE VFTO 40° ASYMMETRICWAT-LIMITED.1 LANDING VREF 40° SYMMETRIC FOR-3° FLIGHT
PATH ANGLE
(1) A combination of weight, altitude and temperature (WAT) such that the thrust or power setting produces the minimum climb gradient specified in § 25.121 for the flight condition.
(2) Airspeed approved for all- engines-operating initial climb.
(3) That thrust or power setting which, in the event of failure of the critical engine and without any crew action to adjust the thrust or power of the remaining engines, would result in the thrust or power specified for the takeoff condition at V 2, or any lesser thrust or power setting that is used for all-engines-operating initial climb procedures.”
25.145(a), (a)(1) Change to read: “It must be possible, at any point between the trim speed prescribed in § 25.103(a)(6) and stall identification (as defined in § 25.201(d)), to pitch the nose downward so that the acceleration to this selected trim speed is prompt with-
(1) The airplane trimmed at the speed prescribed in § 25.103(a)(6);”
25.145(b)(1) - (4) Change “1.4 VS1” to “1.3 VSR1.”
25.145(b)(1) Change “40 percent” to “30 percent.”
Change “stalling speed” to “reference stall speed.”
25.145(b)(6) Change “1.4 VS1” to “1.3 VSR1.”
Change “1.1 VS1” to “VSW.”
Change “1.7 VS1” to “1.6 VSR1.”
25.145(c) Change “1.1 VS1” to “1.08 VSR1.”
Change “1.2 VS1” to “1.13 VSR1.”
25.147(a), (a)(2), (c), (d) Change “1.4 VS1” to “1.3 VSR1.”
25.149(c) Change “1.2 VS” to “1.13 VSR.”
25.161(b), (c)(1), (c)(2), Change “1.4 VS1” to “1.3 VSR1.”
(c)(3), (d)
25.161(e)(3) Change “0.013 VS02” to “0.013VSR02.”
25.175(a)(2), (b)(1), (b)(2), Change “1.4 VS1” to “1.3 VSR1.”
(b)(3), (c)(4)
25.175(b)(2)(ii) Change “VMO + 1.4 VS1/2” to “(VMO + 1.3 VSR1)/2.”
25.175(c) Change speed range to: “...at speeds between V SW and 1.7 VSR1.”
25.175(d) Change speed range to: “...at speeds between V SW and 1.7 VSR0.”
25.175(d)(5) Change “1.4 VS0” to “1.3 VSR0.”
25.177(c) Change “1.2 VS1” to “1.13 VSR1.”
25.181(a), (b) Change “1.2 VS” to “1.13 VSR.”
25.201(a)(2) Change “1.6 VS1” to “1.5 VSR1” and “VS1” to “VSR1.”
Change “stalling speed” to “reference stall speed.”
25.207(c) Change to read: “When the speed is reduced at rates not exceeding one knot per second, in straight flight with engines idling and at the center-of-gravity position specified in § 25.103(a)(5), stall warning must begin, in each normal configuration, at a speed, V SW, exceeding the reference stall speed by not less than three knots or three percent, whichever is greater. Once initiated, stall warning must continue until the angle of attack is reduced to approximately that at which the stall warning began.”
25.207(d) Insert a new paragraph that reads: “In slow-down turns at 1.5g load factor normal to the flight path and airspeed deceleration rates greater than two knots per second, with the flaps and landing gear in any normal position, the stall warning margin must be sufficient to allow the pilot to prevent stalling (as defined in § 25.201(d)) when recovery is initiated not less than one second after the onset of stall warning.”
25.207(e) Insert a new paragraph that reads: “Stall warning must also be provided in each abnormal configuration of the high lift devices likely to be used in flight following system failures (including all configurations covered by Airplane Flight Manual procedures).”
25.233(a), and Change “0.2 VS0” to “0.2 VSR0.”
25.237(a), (b)(1) and (b)(2)
SUBPART D
25.735(f)(2) Change the KE equation to read: “KE = 0.0443(WV 2/N)” Change the V definition to read: “V = V REF/1.3” and “VREF = Airplane steady landing approach speed, in knots, at the maximum design landing weight and in the landing configuration at sea level; and”
25.735(g) Change to read: “The minimum speed rating of each main wheel-brake assembly (that is, the initial speed used in the dynamometer tests) may not be more than the V used in the determination of kinetic energy in accordance with paragraph (f) of this section, assuming...”
25.773(b)(1)(i) Change “1.6 VS1” to “1.5 VSR1.”
SUBPART E
25.1001(c)(1) and (c)(3) Change 1.4 VS1 to 1.3 VSR1.
SUBPART F
25.1323(c)(1) Change “1.3 VS1” to “1.23 VSR1.”
25.1323(c)(2) Change “1.3VS0” to “1.23VSR0.”
25.1325(e) Change “1.3 VS0” to “1.23 VSR0.”
Change “1.8 VS1” to “1.7 VSR1.”
Part 36 (Noise Standa rds:
Aircraft Type and Airworthiness Certification) NOTE: It has been determined that the following is equivalent for the purposes of FAR Part 36 certification.
Appendix C, Sec. C36.9(e)(1) Change “1.30VS + 10 knots” to “VREF + 10 knots.”
FCAA POSITION:
APPLICANT POSITION:
CONCLUSION:
________________________________ _________________________ Transport Airplane Directorate Date
Aircraft Certification Service
APPENDIX 6
SAMPLE FLIGHT TEST PROGRAM [RESERVED]
APPENDIX 7 - FAA HANDLING QUALITIES RATING METHOD
a. Explanation. With the advent of transport category airplanes employing electronic flight control systems (EFCS) that provide control augmentation, and sometimes employ limiting systems, the ability to make a literal finding of compliance with many of the stability and control requirements of Part 25 was eroded. As a result the Handling Qualities Rating Method (HQRM) presented in this appendix was developed to provide a pseudo-quantitative means of evaluating airplane flying qualities. The HQRM draws on a matrix of parameters in defining the desired handling characteristics, including atmospheric conditions, flight envelope conditions, pilot task tracking requirements, and probability of occurrence.
(1) Figure 1 presents a list of deficiencies that exist for applying existing regulations to airplanes with maneuver demand electronic flight control systems.
(2) Since the subject airplanes have redundant EFCS capabilities, which generally provide reduced levels of control duplication with progressive failure states, a "failure consequence vs. probability" type of approach is applicable (see Figure 2).
b. Procedures. The HQRM is to be applied as a task-oriented system to be used in the evaluation of airplane handling qualities in accordance with the following procedures.
(1) A probability of occurrence versus effect philosophy is applied in relating the flight test variables to flight envelope characteristics, atmospheric disturbance levels, and probability of a specific flight control failure state. The combined application of these parameters to make a finding of compliance is shown schematically in Figure 4.
(2) It has also become necessary to create a defined set of criteria by which to evaluate the handling qualities of EFCS-equipped airplanes. In an attempt to create a system that can be used in a standardized manner, the handling qualities rating method has been limited to three levels: Satisfactory (SAT), Adequate (ADQ), and Controllable (CON). These pilot ratings are defined and compared with other established rating scales in Figure 5A. Handling qualities must be demonstrated to meet one of these ratings levels for a particular flight condition that will be defined in terms probability of occurrence, flight envelope, and level of atmospheric disturbance (see Figures 5B, C, and D).
(3) Matrices can be formed of measurable flight parameters for the normal, operational, and limit flight envelopes. These are shown in the "spider web" charts for flaps up and flaps down in Figures 6 and 7, respectively.
(4) A description of the pilot ratings (SAT, ADQ, & CON) is presented in Figure 8 along with their equivalent Cooper-Harper and Military Standard ratings for comparison.
(5) Figure 9 presents the method for combining the various flight condition parameter probabilities that will, in turn, be used to determine the minimum handling qualities rating. This method is shown in a graphical format in Figure 10.
(6) The HQRM is to be used in a task-oriented environment to evaluate airplane handling qualities while performing typical static and dynamic maneuvers. A sample list of such tasks is presented in Figure 11.
(7) Figure 12 shows a table of the minimum FAA handling qualities rating for a given flight condition, defined as a combination of the flight envelope conditions and the level of atmospheric disturbance, relative to the probability of the failure condition being evaluated.
CURRENT BASIC OBJECTIVE LIKELY DEFICIENCY FOR
REGULATION AIRPLANE WITH FBW
MANEUVER DEMAND EFCS
25.171/173/175 Static Long. Stab: Literal noncompliance: Airplane 1 lb/6 kts, average has short-term path stability.
25.171/177 Stat. Lat-Dir Stab: Literal noncompliance for roll- Fa/Beta > 0 rate command EFCS, when airplane in steady sideslip.
25.671(c)(2) Control Systems, General: Proper objective, but no Continued safe flight and structured approach showing landing after combination compliance for matrix of EFCS of failures not shown to failure modes and flight be extremely improbable. conditions.
25.672(c)(1)-(3) Various HQ requirements • Deals only with single failures for failure of stability (e.g., Yaw Damper-only augmentation/power- technology) operated systems. • Presumes controllability and maneuverability requirements can be maintained, yet trim, stability, and stall characteristics can be impaired.
25.1309(b)(1) Occurrence of any failure • Applies to systems, but has condition which would indirect relation to flight prevent continued safe characteristics evaluationflight and landing is clarification needed.
extremely improbable • Differences between U.S. and European airworthiness interpretations.
Figure 1: Airworthiness HQ Regulations Impacted/Outpaced by Technology.