Federal Register, Volume 68 Issue 1 (Thursday, January 2, 2003)

[Federal Register Volume 68, Number 1 (Thursday, January 2, 2003)]
[Notices]
[Pages 149-154]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-33130]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

Proposed Revisions to Advisory Circular 25-7A, Flight Test Guide
for Certification of Transport Category Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed advisory circular revisions and request for
comments.

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SUMMARY: The Federal Aviation Administration (FAA) requests comments on
proposed revisions to Advisory Circular (AC) 25-7A, ``Flight Test Guide
for Certification of Transport Category Airplanes.'' The proposed
revisions provide revised guidance on a means of demonstrating
compliance with the new requirements of part 25 as presented in
Amendment 25-108 (67 FR 70812, November 26, 2002), entitled ``1-g Stall
Speed as the Basis for Compliance with Part 25 of the Federal Aviation
Regulations.'' This notice provides interested persons an opportunity
to comment on the proposed revisions to the AC. The guidance will be
included in the next revision to AC 25-7A.

DATES: Comments must be received on or before March 3, 2003.

ADDRESSES: Send all comments on the proposed AC revisions to the
Federal Aviation Administration, Attention: Don Stimson, Airplane and
Flight Crew Interface Branch, ANM-111, Transport Airplane Directorate,
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, WA 98055-
4056. Comments may be examined at the above address between 7:30 a.m.,
and 4 p.m., except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Jan Thor, Standardization Branch, ANM-
113, at the above address, telephone (425) 227-2127, or facsimile (425)
227-1320.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to comment on the proposed AC
revisions by submitting such written data, views, or arguments, as they
may desire. You must identify the title of the AC and submit comments
in duplicate to the address specified above. The Transport Airplane
Directorate will consider all comments received on or before the
closing date for comments before issuing the revision to the AC. You
may view the complete text of AC 25-7A on the Internet at: http://www.faa.gov/certification/aircraft/air_index.htm, at the link titled
``Advisory Circulars,'' or at the Regulatory and Guidance Library Web
site at http://www.airweb.faa.gov/rgl, at the link titled ``Advisory
Circulars.''

Discussion

By Amendment 25-108 (67 FR 70812, November 26, 2002), the FAA
revised the airworthiness standard for transport category airplanes to
redefine the reference stall speed for transport category airplanes to
a speed not less than the 1-g stall speed instead of the minimum speed
obtained in a stalling maneuver. The FAA took this action to provide
for a consistent, repeatable reference stall speed; ensure consistent
and dependable maneuvering margins; provide for adjusted multiplying
factors to maintain approximately the current requirements in areas
where use of the minimum speed in the stalling maneuver has proven
adequate; and harmonize the applicable regulations with those currently
adopted in Change 15 to the European Joint Aviation

[[Page 150]]

Requirements, JAR-25. The changes provide a higher level of safety for
those cases in which the current methods result in artificially low
operating speeds. To address these new requirements to part 25, the FAA
is proposing to revise AC 25-7A to describe acceptable means of showing
compliance with the new rules.

Proposed Revisions to AC 25-7A

Revise paragraph 3a(3)(i) by replacing ``1.4VS1'' with
``1.3 VSR1'' (three occurrences).
Revise paragraph 3a(3)(ii)(B) by replacing ``.12VS1''
with ``0.11 VSR1.''
Revise paragraph 10b(3)(i)(B) by replacing ``1.2 times
VS'' with ``1.13 times VSR,'' ``VS''
with ``VSR,'' and ``stall speed'' with ``reference stall
speed.''
Revise paragraph 10b(3)(ii) by replacing ``1.15 times
VS'' with ``1.08 times VSR.''
Revise paragraph 10b(4) as follows:
(4) Section 25.107(c)--Takeoff Safety Speed (V2).
V2 is the calibrated airspeed that is attained at or before
the airplane reaches a height of 35 ft. above the takeoff surface after
an engine failure at VEF using an established rotation speed
(VR). During the takeoff speeds demonstration, V2
should be continued to an altitude sufficient to assure stable
conditions beyond the 35 ft. height. V2 cannot be less than
V2MIN. In addition, V2 cannot be less than the
liftoff speed, VLOF, as defined in Sec. 25.107(f). In
accordance with Sec. 25.107(c), V2 in terms of calibrated
airspeed ``* * * may not be less than VR plus the speed
increment attained before reaching a height of 35 feet above the
takeoff surface'' and ``that provides the maneuvering capability
specified in Sec. 25.143(g).'' * * *
Revise Figure 14-1 by replacing ``=1.25 VS''
with ``VFTO.''
Revise paragraph 16b(2) by replacing ``1.3VS0'' with
``VREF.''
Revise paragraph 16b(3) by replacing ``1.3VS0'' with
``VREF'' (two occurrences).
Revise paragraph 17b(6) as follows:
(6) Section 25.121(d) requires that the stall speed for the
configuration used to show compliance with this requirement not exceed
110 percent of the stall speed for the related landing configuration.
This stall speed ratio requirement is to ensure that an adequate margin
above the stall speed in the selected approach configuration is
maintained during flap retraction. To achieve this stall speed ratio
requirement, it is permissible to arbitrarily increase the landing flap
stall speed, VSR0, to show compliance. Of course, the
landing approach speed used to comply with Sec. 25.125(a)(2) must be
based on the declared stall speed and the stall warning requirements of
Sec. 25.207 must be met at the declared stall speed. However, the
Sec. 25.203 stall characteristics requirements must still be met at
the speed at which the stall is identified (as defined in Sec.
25.201(d)). (An alternative to raising the landing flap stall speed,
VSRO, is to simply increase VREF.)
Revise paragraph 19a(2) as follows:
(2) The minimum value of VREF is specified in Sec.
25.125(a)(2) and is intended to provide an adequate margin above the
stall speed to allow for likely speed variations during an approach in
low turbulence. If the landing demonstrations are unable to show the
acceptability of the minimum approach speed, and the tests are
predicated on the use of a higher approach speed, the landing distance
data presented in the AFM must be based upon the higher approach speed.
Revise paragraph 20a as follows:
a. Explanation. The purpose of Sec. 25.143 is to verify that any
operational maneuvers conducted within the operational envelope can be
accomplished smoothly with average piloting skill and without
encountering stall warning or other characteristics that might
interfere with normal maneuvering, or exceeding any airplane structural
limits. Control forces should not be so high that the pilot cannot
safely maneuver the airplane. Also, the forces should not be so light
it would take exceptional skill to maneuver the airplane without over-
stressing it or losing control. The airplane response to any control
input should be predictable to the pilot.
Add a new paragraph 20a(5) to read as follows:
(5) Modern wing designs can exhibit a significant reduction in
maximum lift capability with increasing Mach number. The magnitude of
this Mach number effect depends on the design characteristics of the
particular wing. For wing designs with a large Mach number effect, the
maximum bank angle that can be achieved while retaining an acceptable
stall margin can be significantly reduced. Because the effect of Mach
number can be significant, and because it can also vary greatly for
different wing designs, the multiplying factors applied to
VSR may be insufficient to ensure that adequate maneuvering
capability exists at the minimum operating speeds. To address this
issue, Sec. 25.143(g) was added by Amendment 25-108 to require a
minimum bank angle capability in a coordinated turn without
encountering stall warning or any other characteristic that might
interfere with normal maneuvering. The maneuvering requirements consist
of the minimum bank angle capability the FAA deems adequate for the
specified regimes of flight combined with a further 15 degrees of bank
angle to provide a safety margin for various operational factors. These
operational factors include both potential environmental conditions
(e.g., turbulence, wind gusts) and an allowance for piloting
imprecision (e.g., inadvertent overshoots).
Revise the first sentence of paragraph 20b and reformat paragraph
20b as follows:
b. General Test Requirements. (1) Compliance with Sec. Sec.
25.143(a) through (f) is primarily a qualitative determination by the
pilot during the course of the flight test program. * * *
Add a new paragraph 20b(2) to read as follows:
(2) Since Sec. 25.143(g) involves a target speed, bank angle, and
maximum value of thrust, not all flight test conditions to demonstrate
compliance will necessarily result in a constant-altitude, thrust-
limited turn. In cases with positive excess thrust, a climbing
condition at the target bank and speed is acceptable. Alternately, if
desired, the thrust may be reduced to less than the maximum allowed, so
that compliance is shown with a completely stabilized, constant-
altitude turn. For cases with negative excess thrust (e.g., the landing
configuration case), a constant-altitude slow-down maneuver at the
target bank angle has been shown to be a suitable technique. With the
airplane descending at VREF in wings-level flight on a three
degree glide path, trim and throttle position is noted. The airplane is
then accelerated to VREF + 10-20 knots in level flight. The
original trim and throttle conditions are reset as the airplane is
rolled into a constant-altitude slow-down turn at the target bank
angle. Throttles can be manipulated between idle and the marked
position to vary slow-down rate as desired. Compliance is shown when
the airplane decelerates through VREF in the turn without
encountering stall warning. Revise paragraph 20c(2) by replacing ``1.3
VS'' with ``1.23 VSR.'' Add a new paragraph
20f(2)(v) to read as follows:
(v) Thrust or Power Setting for Maneuver Capability Demonstrations.
The effect of thrust or power on maneuver capability is normally a
function of only the thrust-to-weight ratio. Therefore, for those
configurations in which the weight, altitude, temperature (WAT)-limited
thrust or power setting is prescribed, it is usually acceptable to use
the thrust or power setting that is consistent with a WAT-limited climb
gradient at the test

[[Page 151]]

conditions of weight, altitude, and temperature. However, if the
maneuver margin to stall warning (or other characteristic that might
interfere with normal maneuvering) is reduced with increasing thrust or
power, the critical conditions of both thrust or power and thrust-to-
weight ratio must be taken into account when demonstrating the required
maneuvering capabilities. Revise paragraph 21a(1) as follows:
Section 25.145(a) requires that there be adequate longitudinal
control to promptly pitch the airplane nose down from at or near the
stall to return to the original trim speed. The intent is to ensure
sufficient pitch control for a prompt recovery if inadvertently slowed
to the point of stall. Although this requirement must be met with power
off and at maximum continuous thrust or power, there is no intention to
require stall demonstrations with thrust or power above that specified
in Sec. 25.201(a)(2). Instead of performing a full stall at maximum
continuous power or thrust, compliance may be assessed by demonstrating
sufficient static longitudinal stability and nose down control margin
when the deceleration is ended at least one second past stall warning
during a one knot per second deceleration. The static longitudinal
stability during the maneuver and the nose down control power remaining
at the end of the maneuver must be sufficient to assure compliance with
the requirement. Revise paragraph 21b(1)(ii) as follows:
(ii) Test procedure: The airplane should be trimmed at the speed
for each configuration as prescribed in Sec. 25.103(b)(6). * * *
Revise paragraph 21b(2)(ii) by replacing ``1.4VS'' with
``1.3 VSR'' (two occurrences).
Revise paragraph 21b(3)(ii) by replacing ``1.4VS'' with
``1.3 VSR'' (two occurrences).
Revise paragraph 21b(4)(ii) by replacing ``1.4VS'' with
``1.3 VSR'' (two occurrences).
Revise paragraph 21b(5)(ii) by replacing ``1.4VS'' with
``1.3 VSR,'' ``1.1VS'' with ``VSW,''
and ``1.7VS'' with ``1.6 VSR.''
Revise paragraphs 21b(6)(i)(E) and 21b(6)(ii) by replacing
``1.1VS'' with ``1.08 VSR'' and
``1.2VS'' with ``1.13 VSR.''
Revise paragraph 22b(1)(i)(F) by replacing ``1.4VS''
with ``1.3 VSR.''
Revise paragraph 22b(2)(i)(F) by replacing ``1.4VS1''
with ``1.3 VSR1.''
Revise paragraph 22b(3)(ii) by replacing ``1.4VS'' with
``1.3 VSR'' and ``1.4VS1'' with ``1.3
VSR1.''
Revise paragraph 23b(2)(ii)(A) by replacing ``1.2VS''
with ``1.13 VSR.''
Revise paragraph 23b(2)(iii)(B) by replacing ``1.1VS''
with ``1.08 VSR.''
Revise paragraphs 27a(1), (2), and (3)(i) by replacing
``1.2VS1'' with ``1.13 VSR1.''
Revise paragraph 28a(1) by replacing ``1.2VS1'' with
``1.13 VSR1.''
Revise paragraph 29b(1)(i) as follows:
(i) To define the reference stall speeds and how they vary with
weight, altitude, and airplane configuration. Revise paragraph 29b(2)
as follows:
(2) During this testing, the angle-of-attack should be increased at
least to the point where the behavior of the airplane gives the pilot a
clear and distinctive indication through the inherent flight
characteristics or a stall identification device (e.g., stick pusher)
that the airplane is stalled.
Revise paragraph 29b(3) as follows:
(3) The airplane is considered to be fully stalled when any one or
a combination of the characteristics listed below occurs to give the
pilot a clear and distinctive indication to cease any further increase
in angle of attack, at which time recovery should be initiated using
normal techniques.
Revise paragraph 29c(1) as follows:
(1) Background. (i) Since many of the regulations pertaining to
performance and handling qualities specify trim speeds and other
variables that are functions of stall speeds, it is desirable to
accomplish the stall speed testing early in the program, so the data
are available for subsequent testing. Because of this interrelationship
between the stall speeds and other critical performance parameters, it
is essential that accurate measurement methods be used. Most standard
airplane pitot-static systems have not been found to be acceptable for
stall speed determination. These tests require the use of properly
calibrated instruments and usually require a separate test airspeed
system, such as a trailing bomb, a trailing cone, or an acceptable nose
or wing boom.
(ii) Prior to Amendment 25-108, the stall speed defined in Sec.
25.103 was the minimum speed attained in the stalling maneuver. For
many high speed swept wing transport category airplanes the resulting
stall speed often occurs at a load factor normal to the flight path
considerably less than one, which leads to inconsistent and
unrepeatable reference stall speeds. Pilot technique can also
significantly influence the rate and magnitude of any spontaneous nose
down pitch occurring at the stall, thereby contributing to
inconsistencies in the determination of the minimum speed obtained in
the stalling maneuver. Since Part 25 defines operating speeds as
multiples of the stall speed, the resulting operating speed margins to
stall may not be representative of the actual lift margin available
(i.e., the margin to the speed at which wing lift alone can support the
weight of the airplane in 1-g flight); the net result of this
inadequate lift margin being inconsistent operating speed margins and
maneuvering margins. To ensure that operating speed and maneuvering
margins are directly related to wing lift margin, Amendment 25-108
redefined the reference stall speed as the 1-g stall speed, which is
the speed at which the wing is generating maximum usable lift in a 1-g
flight condition.
(iii) Since the 1-g stall speed is generally higher than the
minimum speed obtained in the stalling maneuver, retaining the existing
multiplying factors for determining the minimum operating speeds would
have resulted in higher minimum operating speeds. However, increasing
the minimum operating speeds could have imposed costs on operators
because of a reduction in payload capability to comply with the
regulations at the higher operating speeds. Based on the service
experience of the transport airplane fleet, the costs imposed would not
have been offset by a commensurate increase in safety. A survey of
various swept wing transport category airplanes was conducted to come
up with revised multiplying factors that would provide essentially the
same operating speeds regardless of the basis used for determining the
reference stall speeds. From the survey, the average load factor at the
minimum speed obtained in the stalling maneuver was determined to be
0.88, which means that the minimum speed obtained in the stalling
maneuver was, on average, 94 percent of the 1-g stall speed. For that
reason, in Amendment 25-108 the multiplying factors applied to the
reference stall speed were reduced by approximately six percent.
(iv) Although the reduced multiplying factors were intended to
result in roughly equivalent operating speeds, there is one class of
airplanes for which a significantly lower operating speed would be
obtained. Airplanes equipped with a device that abruptly pushes the
nose down (e.g., a stick pusher) near the angle of attack for maximum
lift would be operated at speeds and angles-of-attack closer to the
pusher activation point than has been experienced in operational
service. For these airplanes, the minimum speed obtained in the
stalling maneuver is closer to 96 to 97 percent of the 1-g stall speed.
Therefore, to maintain equivalency in operating speeds for these
airplanes, a supplementary margin has been

[[Page 152]]

established such that VSR must not be less than the greater
of 2 knots or 2 percent above the speed at which the device activates.
In addition, see paragraph 228 of this AC for guidance material
regarding the design and function of such systems.
Revise paragraph 29c(3)(i) as follows:
(i) The airplane should be trimmed for hands-off flight at a speed
13 percent to 30 percent above the anticipated VSR with the
engines at idle and the airplane in the configuration for which the
stall speed is being determined. Then, using only the primary
longitudinal control for speed reduction, a constant deceleration
(entry rate) is maintained until the airplane is stalled, as defined in
Sec. 25.201(d) and paragraph 29b(3) of this AC. Following the stall,
engine thrust may be used as desired to expedite the recovery.
Revise paragraph 29c(3)(ii) as follows:
(i) A sufficient number of stalls (normally four to eight) should
be accomplished at each critical combination of weight, c.g., and
external configuration. The intent is to obtain enough data to define
the stall speed at an entry rate of 1.0 knot/second.
Revise paragraph 29c(4) as follows:
(4) Thrust Effects on Stall Speed. (i) Stall speeds are typically
determined with the thrust levers at idle; however, it is necessary to
verify by test or analysis that engine idle thrust does not result in
stall speeds that are appreciably lower than would be obtained at zero
thrust. Prior to Amendment 25-108, a negative thrust at the stall,
which slightly increases stall speeds, was considered acceptable, but
it was not required to be taken into account. With the adoption of
Amendment 25-108, it became a requirement to take into account idle
thrust except where that thrust level results in a significant decrease
in stall speed.
(ii) To determine whether thrust effects on stall speed are
significant, at least three stalls should be conducted at one flap
setting, with thrust set to approximately the value required to
maintain level flight at 1.5 VSR in the selected
configuration.
(iii) These data may then be extrapolated to a zero thrust
condition to determine the effect of idle thrust on stall speeds. (See
Figure 29-1.) If the difference between idle thrust and zero thrust
stall speed is 0.5 knots or less, the effect may be considered
insignificant.
(iv) The effects of engine power on stall speeds for a
turbopropeller airplane can be evaluated in a similar manner. Stall
speed flight tests should be accomplished with engines idling and the
propellers in the takeoff position. Engine torque, engine r.p.m., and
estimated propeller efficiency can be used to predict the thrust
associated with this configuration.
Revise paragraph 29c(5) as follows:
(5) Data Reduction and Presentation. The following is an example of
how the data obtained during the stall speed testing may be reduced to
standard conditions. Other methods may be found acceptable.
(i) Indicated airspeed from the flight test airspeed system is
recorded throughout the stall, and these values are corrected to
equivalent airspeed. Load factor normal to the flight path must also be
recorded. Typically the load factor data would be obtained from a
sufficient number of accelerometers capable of resolving the flight
path load factor. At the bare minimum, one accelerometer aligned along
the expected 1-g stall pitch angle may provide acceptable data.
(ii) The airplane corrected lift coefficient
(CLCORR) is calculated from the equation given
below and plotted as a time history throughout the stall.
[GRAPHIC] [TIFF OMITTED] TN02JA03.028

Where:

nzw = airplane load factor normal to the flight path
W = airplane test weight--lbs.
q = dynamic pressure--lbs./ft. ²
S = reference wing area--ft. ²
V = knots equivalent airspeed.

(iii) The maximum lift coefficient (CLMAX) is defined as
the maximum value of CLCORR achieved during the stall test.
Where the plot of CLCORR exhibits multiple peak values,
CLMAX corresponds to the first maximum. There should also
typically be a noticeable break in a plot of the load factor normal to
the flight path near the point at which CLMAX is reached.
The analysis to determine CLMAX should disregard any
transient or dynamic increases in recorded load factor, such as might
be generated by abrupt control inputs, that do not reflect the lift
capability of the airplane. The load factor normal to the flight path
should be maintained at nominally 1.0 until CLMAX is
reached. (See Figure 29-1.)
(iv) The CLMAX obtained for each stall is then
corrected, if necessary, from the test c.g. position to the targeted
c.g. position using the equation:
[GRAPHIC] [TIFF OMITTED] TN02JA03.029

Where

MAC= Wing mean aerodynamic chord length--inches.
1t = Effective tail length, measured between the wing 25
percent MAC and the stabilizer 25 percent MAC--inches.
CGstd = C.G. position resulting in the highest value of
reference stall speed (normally the forward c.g. limit at the pertinent
weight)--percent MAC/100
CGtest = Actual test c.g. position--percent MAC 100
[Delta]CLT = Change in CL due to
engine thrust (if significant).

(v) Stall entry rate, which is defined as the slope of a straight
line connecting the stall speed and an airspeed 10 percent above the
stall speed, should be determined for each stall test. Because
CLMAX is relatively insensitive to stall entry rate, a
rigorous investigation of entry rate effects should not be necessary.
Test data should bracket a 1.0 knot/second entry rate such that the
value of CLMAXCG corresponding to an entry rate
of 1.0 knot/second can be determined. This value of
CLMAXCG should be used to determine the reference
stall speed defined in Sec. 25.103(a).
(vi) For each approved configuration, a plot of CLMAX
versus weight is constructed. (See Figure 29-2.) An initial negative
slope of this plot may be caused by several factors:
(A) A decrease in CLMAX due to increasing Mach number (which
increases as the stall speed goes up with weight);
(B) The fact that CLMAX is proportional to the rate of
change of angle of attack, whereas the data are plotted at a fixed
airspeed bleed rate; and
(C) Minor adverse aeroelastic effects on the wings and high lift
devices as weight (and therefore speed) increases. An inflection in the
plot is typically caused by a variation in the forward c.g. limit with
weight.
(vii) In the measurement of stall speeds, the lowest test altitude
is usually dictated by flight test safety concerns. This test data must
then be expanded to lower altitudes, and hence, lower Mach numbers to
cover the operational envelope of the airplane. Since CLMAX
increases as the Mach number is reduced, simple expansion of the flight
test data could result in extrapolating to a higher CLMAX
than tested. Expansion of CLMAX versus Mach number data is
only permitted up to the highest CLMAX within the range of
W/[b.delta]'s tested.
(viii) The reference stall speed is a calibrated airspeed, not less
than the 1-g stall speed, and is expressed as:

[[Page 153]]

[GRAPHIC] [TIFF OMITTED] TN02JA03.030

Where:

VCLMAX =
[GRAPHIC] [TIFF OMITTED] TN02JA03.031

If the stalling maneuver is limited by a device that commands an
abrupt nose down pitch (e.g., a stick pusher), VCLMAX may
not be less than the speed existing at the instant the device operates.
[Delta]VC = compressibility correction (i.e., the difference
between equivalent airspeed and calibrated airspeed).
W = airplane weight--lbs.
CLMAX = value of CLMAX corresponding to the
chosen weight (see Figure 29-3).
S = reference wing area--ft \2\.

(ix) For airplanes equipped with a device that abruptly pushes the
nose down at a selected angle-of-attack (e.g., a stick pusher), VSR
must not be less than the greater of 2 knots or 2 percent above the
speed at which the device activates.
(x) In showing compliance with Sec. 25.103(d), in the case where a
device that abruptly pushes the nose down at a selected angle of attack
(e.g., a stick pusher) operates after CLMAX, the speed at
which the device operates need not be corrected to 1 g. Otherwise, it
would be possible for the device activation speed to be assessed as
higher than VSR (or at least closer to VSR than would be obtained
without correcting for load factor). Requiring the correction of the
device activation speed to the 1-g condition would unnecessarily
increase the stringency of Sec. 25.103(d). Test procedures should be
in accordance with paragraph 29c(3)(i) to ensure that no abnormal or
unusual pilot control input is used to obtain an artificially low
device activation speed.
Revise paragraph 29d(2)(v) as follows:
(v) For power-on stalls, thrust should be set to the value required
to maintain level flight at a speed of 1.5 VSR at maximum landing
weight with flaps in the approach position, and the landing gear
retracted. The approach flap position referred to is the maximum flap
deflection used to show compliance with Sec. 25.121(d), which
specifies a configuration in which the reference stall speed does not
exceed 110 percent of the reference stall speed for the related landing
configuration.
Revise paragraph 29d(2)(ix) as follows:
(ix) For abnormal aerodynamic configurations covered by AFM
procedures, high angle-of-attack characteristics should be evaluated
down to either stall warning, or to an angle-of-attack equivalent to
the AFM recommended landing approach speed divided by 1.23. * * *
Revise paragraph 29d(3) as follows:
(3) Procedures. (i) The airplane should be trimmed for hands-off
flight at a speed 13 percent to 30 percent above the reference stall
speed, with the appropriate power setting and configuration. Then,
using only the primary longitudinal control, establish and maintain a
deceleration (entry rate) consistent with that specified in Sec. Sec.
25.201(c)(1) or 25.201(c)(2), as appropriate, until the airplane is
stalled. Both power and pilot selectable trim should remain constant
throughout the stall and recovery (angle of attack has decreased to the
point of no stall warning).
(ii) The same trim reference (for example, 1.23 VSR) should be used
for both the stall speeds and characteristics testing. For all stall
testing, the trim speed is based on the performance stall speeds
provided in the AFM.
Revise paragraph 29f(2) as follows:
(ii) Timeliness. For one knot per second entry rate stalls, the
stall warning must begin at a speed, VSW, not less than five knots or
five percent CAS (whichever is greater) above the speed at which the
stall is identified in accordance with Sec. 25.201(d). For straight
flight stalls, at idle thrust and with the center-of-gravity at the
position specified in Sec. 25.103(b)(5), the stall warning must begin
at a speed not less than three knots or three percent (whichever is
greater) above the reference stall speed. These speed margins should be
in terms of the same units of measurement as VSR (i.e., calibrated
airspeed).
(iii) Consistency. The stall warning must be reliable and
repeatable. The warning must occur with flaps and gear in all normally
used positions in both straight and turning flight and must continue
throughout the stall demonstration until the angle of attack is reduced
to approximately that at which the stall warning was initiated. The
warning may be furnished naturally through the inherent aerodynamic
characteristics of the airplane, or artificially by a system designed
for this purpose. If artificial stall warning is provided for any
airplane configuration, it must be provided for all configurations.
Add paragraph 29f(2)(vi) as follows:
(vi) If the stall warning required by Sec. 25.207 is provided by
an artificial stall warning system (e.g., a stick shaker), the effect
of production tolerances on the stall warning system should be
considered when evaluating the stall warning margin required by
Sec. Sec. 25.207(c) and (d) and the maneuver capabilities required by
Sec. 25.143(g).
(A) The stall warning margin required by Sec. Sec. 25.207(c) and
(d) should be available with the stall warning system set to the most
critical setting expected in production. Unless another setting would
provide a lesser margin, the stall warning system should be operating
at its high angle of attack limit. For airplanes equipped with a device
that abruptly pushes the nose down at a selected angle-of-attack (e.g.,
a stick pusher), the stall warning margin may be evaluated with both
the stall warning and stall identification (e.g., stick pusher) systems
at their nominal angle of attack settings unless a lesser margin can
result from the various system tolerances.
(B) The maneuver capabilities required by Sec. 25.143(g) should be
available assuming the stall warning system is operating on its nominal
setting. In addition, when the stall warning system is operating at its
low angle of attack limit, the maneuver capabilities should not be
reduced by more than 2 degrees of bank angle from those specified in
Sec. 25.143(g).
(C) The stall warning margin and maneuver capabilities may be
demonstrated by flight testing at the settings specified above for the
stall warning and, if applicable, stall identification systems.
Alternatively, compliance may be shown by applying adjustments to
flight test data obtained at a different system setting.
Revise paragraph 29f(3) as follows:
(3) Procedures. Stall warning tests are normally conducted in
conjunction with the stall testing required by Sec. Sec. 25.103 (stall
speeds), 25.201 (stall demonstration), and 25.203 (stall
characteristics), including consideration of the prescribed bank
angles, power settings, and center-of-gravity position. In addition, if
the stall warning margin may be affected by a system (e.g., a stall
warning or stick pusher system that modifies the stall warning or stall
identification speed as a function of thrust, bank angle, angle-of-
attack rate, etc.), compliance with Sec. 25.207(c) should be
demonstrated at the most critical conditions in terms of stall warning
margin. However, bank angles greater than 40 degrees and power or
thrust exceeding maximum continuous power or thrust need not be
demonstrated. If the effect of the stall identification or stall
warning system compensation is to increase the stall warning margin
relative to the nominal values demonstrated during the testing required
by Sec. Sec. 25.103, 25.201, and

[[Page 154]]

25.203, no further stall warning margin demonstrations need to be done.
Revise paragraph 29f(4) as follows:
(4) Data Acquisition and Reduction. The stall warning speed and
type and quality of warning should be noted. The speed at which
acceptable stall warning begins should then be compared to the stall
identification speed and, for the conditions under which VSR is
defined, VSR, to determine if the required margin exists. The stall
warning speed margin required by Sec. 25.207(d) should be determined
at a constant load factor.
Revise paragraph 29g as follows:
g. Accelerated Stall Warning. (1) Explanation. Section 25.207(e)
requires that, in slow-down turns with at least a 1.5g load factor
normal to the flight path and an airspeed deceleration rate greater
than 2 knots per second, sufficient stall warning is provided to
prevent stalling when the pilot takes recovery action not less than one
second after recognition of stall warning. The purpose of the
requirement is to ensure that adequate stall warning exists to prevent
an inadvertent stall under the most demanding conditions that are
likely to occur in normal flight. The conditions of 1.5g and an
airspeed deceleration rate greater than 2 knots per second correspond
to the steep turn maneuver prescribed in Part 121, Appendices E and F
for pilot initial and proficiency training, respectively, plus some
margin for error (3 degrees more bank and a decreasing airspeed). The
elevated load factor will emphasize any adverse stall characteristics,
such as wing drop or asymmetric wing flow breakdown, while also
investigating Mach and potential aeroelastic effects on available lift.
The greater than 2 knot per second deceleration rate is intended to
result in a reasonable penetration beyond the onset of stall warning.
(2) Procedures. (i) Trim at 1.3 VSR. Once trimmed,
accelerate to a speed that will allow enough time to set up and
complete the maneuver at the specified load factor and airspeed
deceleration rate. Power or thrust should be set appropriate to the
power for level flight at 1.3 VSR and not adjusted during
the maneuver. In a level flight maneuver, 1.5g equates to a bank angle
of 48 degrees. To prevent an excessive deceleration rate (e.g., greater
than 3 knots per second), a descent may be used. Conversely, if the
deceleration rate is too low, the maneuver should be conducted in a
climbing turn.
(ii) After the onset of stall warning, continue the maneuver
without releasing stick force for one second before attempting
recovery. Normal low speed recovery techniques should be used. If any
of the indications of a stall prescribed in Sec. 25.201(d) (see
paragraph 29b(3) of this AC) occur during the accelerated stall warning
demonstration, compliance with Sec. 25.207(d) will not have been
demonstrated.
Revise paragraph 29h as follows:
h. Maneuver Margins. See paragraph 20 of this AC for guidance
material associated with demonstrating compliance to the maneuvering
capability requirements of Sec. 25.143(g).
Redesignate existing paragraph 29i as 29j and add a new paragraph
29i as follows:
i. Tolerance Considerations for Airplanes Equipped with Stall
Identification Systems. For airplanes equipped with a stall
identification device, the applicant should consider the combined
effects of the variables listed in paragraphs (1) through (4) below to
determine the critical configuration for stall testing. A maximum
deviation in stall speed of +-1 knot, from that defined in the nominal
configuration, is considered acceptable for the combined effects of the
items listed in paragraphs (1) through (3). The deviation in stall
speed due to stall identification system tolerances (paragraph 3),
alone, should not exceed +-0.5 knots. (The stall identification system
consists of everything from the angle of attack sensing device to the
connection of the force application actuator to the longitudinal
control system.) It should be verified that threshold tolerances and
system design features (e.g., filtering, phase advancing) will not
result in an unsafe diminishing of the margin between stall warning and
pusher activation, or pusher activation and some dangerous airplane
characteristic. Investigations should include the demonstration of
maneuver margins, dynamic stall entries, the effects of atmospheric
turbulence, and operation in windshear environments where the airplane
will be flown at, or very near, stall warning. These flying conditions
should not result in unwanted activation of the stall identification
system or aerodynamic stall prior to, or close to, activation of the
stall warning system. This verification may be provided by a
combination of analysis, simulation, and flight test.
(1) High lift device and control surface rigging--at the limits of
their respective tolerance bands that is most detrimental to the
production of lift;
(2) Airframe build tolerances--the impact of wing angle of
incidence variation relative to stall identification system vane angle;
(3) Stall identification system tolerances--activation vane angles
should be at the low end of the tolerance band for stall speed testing,
and at the high end for stall characteristics testing; and
(4) Wing leading edge condition--the effect of wing leading edge
contamination (e.g., insects) on stall speeds should be determined and
accounted for if significant. The critical height and density of the
contaminant should be substantiated by Generic. This testing may be
accomplished using an artificial contaminant.
Remove existing Figure 29-1, renumber Figure 29-5 as Figure 29-1,
add a new Figure 29-2, and reorder the remaining figures appropriately.
Revise paragraphs 30c(2)(i), 30e(1)(iii), and 30e(2)(ii) by
replacing ``VS0'' with ``VSR0.''
Revise Page 2 of Appendix 4 by replacing ``1.2VS'' with
``1.13 VSR'' (two occurrences).
Remove Appendix 5.

Issued in Renton, Washington, on December 20, 2002.
Vi L. Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification
Service, ANM-100.
[FR Doc. 02-33130 Filed 12-31-02; 8:45 am]
BILLING CODE 4910-13-P