MIL-DTL-9490E
f. Performance tolerances of automatic control systems operating concurrently with the
AFCS all weather landing system; e.g., stability augmentation systems, load alleviation systems.
3.1.2.10.2 Performance standards - ground based equipment variations. Proof of
compliance with performance requirements for all weather landing systems shall include the
effects of expected variation in type and quality of the ground based equipment. ILS beam
structure, associated tolerances and alignment errors, monitoring, touchdown zone lighting, terrain
clearances, and controlled or critical taxi zones shall be considered to meet the requirements for
Categories II or III operations as defined by ICAO Annex 10.
3.1.2.11 Flight load fatigue alleviation. A fatigue alleviation control system may be used
where it is advantageous to the weapon system. The fatigue alleviation system shall comply with
applicable requirements of MIL-A-8866 in addition to the requirements of this specification.
3.1.2.12 Ride smoothing. With the ride smoothing AFCS and other FCS in
Operational State I, the following short term and applicable long term vertical or lateral axis ride
discomfort index levels shall not be exceeded at any crew station during flight in the turbulence
level specified in table II. The requirements apply separately to each of the vertical and lateral axes.
For the lateral axis requirement only lateral gusts apply and for vertical acceleration only vertical
gusts apply. Effects of attitude hold or other pertinent AFCS modes shall be included where used.
This requirement normally applies only where a ride smoothing AFCS is specified by the
procuring activity. However, where ride smoothing is not specified and other AFCS modes
degrade ride quality, the resulting ride shall not degrade to below the levels specified.
TABLE II. Ride discomfort index limits.
Ride discomfort
Flight Phase Duration
Probability of Exceeding
(Exposure Time)
RMS Turbulence Intensity
Index Di
0.10
Over 3 hours
0.20
Long Term
Requirements
0.13
From 1.5 to 3 hours
0.20
0.20
From 0.5 to 1.5 hours
0.20
Short Term
0.28
Less than 0.5 Hour
0.01
Requirement
3.1.2.12.1 Ride discomfort index. Ride discomfort index is defined as:
1/ 2
⎡ ft
⎤
W ( f ) ⋅ Tcs ( f ) Φμ ( f )df ⎥
⎢∫
2
2
Di
=
⎢0.1
⎥
⎣
⎦
Di
-
Ride Discomfort Index (vertical or lateral)
W( f )
-
Acceleration weighting function (vertical or lateral) 1/g
Tcs( f )
-
Transmissibility, at crew station, g/ft/sec
16
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