AC NO: 91-6~ .- DATE: 5p4b8 .
ADVI SOR’Y
CIRCULAR - DEPARTMENT OF TRANSPORTATION FEDERAL AVlAllOW ADMINISTRATION SUBJECT: WA=, SLUSH, AND SNOW ON THE RUNWAY 1 PURPOSE. This advisory circular is issued to provide information, gkidelines, and recommendations concerning the operation of turbojet aircraft when water, slush, and snow are on the runway.
2 l CANCELLATDN. AC 91-6, dated January 21, 1965, is canceled.
3 0 RACKGROUND.
a. Early in the operation of turbojet aircraft, it was determined that adjustment factors should be applied to the takeoff data in order to mftir tain the aircraft performance requirements as specified in the S&&22 series of the Civil Air Regulations and the Federal. Aviation Regulations when water, slush, and/or snow are on the runway. The first test, using a Boeing 707 airplane, with slush depth of 6/10 inch on the runway, showed that retardation of acceleration on takeoff was of such consequence that an offload from the maximum gross weight should be made for a critical field length.
b In August 1961, further slush tests were conducted at the National Aviation Facilities Experimental Center (NAFEC) by the Federal Aviation Agency/k?ational Aeronautics and Space Administration using the agency's Convair 880/22&I type transport. The test was designed to obtain data regarding the retardation effects of slush and the effects of aquaplaning on the aircraft% takeoff performance, as well as aircraft control problems and damage encountered when operating in a runway slush entizxxunent.
C. Ihe tests at NAFEC were conducted on a slush covered section of a lO,OOO-foot runway at depths of 0 to 2.0 inches and at velocities of 80 to 160 hots. The retardation forces measured from the deceleration data were considerably greater than those predicted from earlier wheel and tire drag tests and theoretical studies which neglected the factors of slush spry impingementandaquaplaning. Impingement of slush against the aircraft and landing wheels contributed significantly to slush drag forces. At Initiated by: ~~~223
AC 9106A 5/Z/78 velocities above 120 knots, aquaplaning occurred and as a result, drag forces were reduced.
4 . GUIDELINES AND RECOMMENDATIONS. The following guidelines and recommendations are provided for those situations where an aircraft takes off on runways with standing water, slush, and/or snow:
a. Takeoffs should not be attempted when standing water, slush, or wet snow greater than l/2 inch in depth covers an appreciable part of the runway.
b 0 The Federal Aviation Regulations concerned with an aircraft's takeoff and landing performance and airplane flight manual requirements are predicated on clean, dry runways. Therefore, certain adjustment factors should be applied to the takeoff data when operating in wet snow, slush, or standing water in depths up to l/2 inch.
c. Many aircraft manufacturers have provided, in appropriate aircraft manuals, adjustment factors to be applied to the takeoff performance data in the FAA-approved flight manual for varying runway conditions. These adjustment factors may include an increase in the required runway for takeoff, a penalty in runway limited weight, and adjustment to the VL speed. The adjustment factors for the runway conditions specified in the applicable operators* manual or flightcrew operating manual should be considered when determining takeoff performance for takeoffs being conducted with water, slush, and/or snow on the runway.
d 0 At the present time, there are no validated engineering data available on which to establish accurate adjustment factors; however, a considerable amount of information and experience has been accumulated and is available to operators. The following tables show examples of adjustments currently being used by operators which are consistent with tests conducted by the agency, These tables have been extracted from the manufacturers' airplane operators manual/flightcrew operating manual as examples of the adjustment factors to be applied for takeoff with water, slush, and/or snow on the runway.
J3-727 / I Vl REIDUC'ITON - K'IS - 29 27 27 28 27 26 u_LI 26 25 - 31 28 a 26 - FIGURE 1 (See appropriate aircraft flight manual for the correct information.)
Page 2 Par 3
5/a/78 AC 91-6~ r‘l 25 25 25 26 27 25 25 25 - 26 25 21, 2lt - FIGURE 2 .
(See appropriate aircraft flight manual for the Correct information.)
J LUSH OR ST!ANDINGWAT!EB DEPTH FIGURE 3 (See appropriate aircraft flight manual for the correct information.)
NOTE: For takeoffs in slush or standing water, reduce the normal runway limited takeoff gross weight by the appropriate amount shown in Figure 3.
The weight reduction figures shown in Figure 3 reflect the effect of may condition on all-engine operating performance. (F L 0 0 = field length) Par 4 Page 3
AC 91-6A S/&/78 SeaImel 4 Who00 wma 263,ooO m9,m 230,ooO * * m4,3a * Not Vmcg NOE: See ,_-- ‘i / FIGURE 4 (See appropriate aircraft flight manual for the correct information.)
Limited B-707 Operations Manual for V1 speed reductions.
(Se appmpriate aircraft flight manual for the correct information.)
NOTEI 1: In all applicable cases ) V1 reductions are based on minimum VI equal to Vmcg.
NO!IE 2: Vmcg is based on actual ambient conditions.
Page k par 4
DEP'M = l/2 INCH TREMJC~~(lOOO LB) TAKEOFFFIELD,ISNGTH@EET) 7@c9 8,ooo 9,m 10,ooo - 11,ooo 12,m l3,ooo l&o00 FIGUIB 6 (se appropriate aircraft flight manual for the correct information.\ NOTE : The above performance infonaation charts are only samples and should not be used in computing takeoff data. All performance data should be obtained from the appropriate charts in the manufacturers9 operations/flightcrew operating manual for the specific model, engine power, and type aircraft operated.
par 4 page 5
AC 914A 5p4/%3
e. The operations manual of the air carrier and commercial operator or other appropriate documents for general aviation aircraft should include specific instructions for the flightcrew on each type of turbojet aircraft showing the gross weight reduction, V1 speed adjustments, and/or additional runway length required for the conditions described. These instructions should outline details of the methods to be used in determining runway conditions at departw'e time.