AC NU: 91-6A DATE: 5/24/78
WENT OF TRANSPORT
ADVISORY
AND STATES OF AL CIRCULAR
DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION SUBJECT: WATER, SLUSH, AND SNOW ON THE RUNWAY PURPOSE • This advisory circular is issued to provide information, guidelines, and recommendations concerning the operation of turbojet aircraft when water, slush, and snow are on the runway.
20 CANCELLATION. AC 91-6, dated January 21, 1965, is canceled.
BACKGROUND.
a. Early in the operation of turbojet aircraft, it was determined that adjustment factors should be applied to the takeoff data in order to maintain the aircraft performance requirements as specified in the SR-422 series of the Civil Air Regulations and the Federal Aviation Regulations when water, slush, and/or snow are on the rumway. 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/National Aeronautics and Space Administration using the agency's Convair 880/22M type transport. The test was designed to obtain data regarding the retardation effects of slush and the effects of aquaplaning on the aircraft's takeoff performance, as well as aircraft control problems and damage encountered when operating in a runway slush environment.
The tests at NAFEC were conducted on a slush covered section of a 10,000-foot runway at depths of 0 to 2.0 inches and at velocities of 80 to 160 knots. 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 spray impingement and aquaplaning. Impingement of slush against the aircrait and landing wheels contributed significantly to slush drag forces. At Initiated by: AFS-223
velocities above 120 knots, aquaplaning occurred and as a result, drag forces were reduced.
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 1/2 inch in depth covers an appreciable part of the runway.
b. 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 1/2 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 Vi 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. 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 Dy 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 B-727 1/4 INCH SLUSH CORRECTIONS RUNWAY WEICHT REDUCTION - LB (KG V1 REDUCTION - KIS LENGTH FLAPS 5 FLAPS 15 FLAPS 20, 25 FLAPS 5. FLAPS 20,25 FT S.L. 4000 S.L. 4000 S.L. 4000 SoL. D4908 S.L. 4000 12000 12000 15000 14000 16000 1500 5000 (5500 (5500) (7000) (6500) (7500) (7000) 33 32 31 500 13000 17000 16000 7000 ( 6500) (6000) (3000) (7500) (8000) 30 29 29 28 11000 9000 (7500) 18000 17000 17000 (7500) 1500 16000 10000) (8000) (9000) 18000 20000 (10500) (9500) 24000 21000 (10000) (9000) 20000 22000 29 28 27 27 27 26 27 26 13000 (8000) 1800 (11000) 24000 (10000) 22000 26 25 FIGURE 1 (See appropriate aircraft flight manual for the correct information.)
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B-727 1/2 INCH SLUSH CORRECTIONS
RUNWAY WEIGHT REDUCTION - LB KG VI REMOTION - KIS LENGTH FLAPS 5 FLAPS 15 FLAPS 20,25 FLAPS 5,115 g FLAPS 20,25 ET SaL. 4000 4000 S.L. 4000 S.L. 4000 4000 5000 (9000) 20000 (9000) 20000 (10000) 3200¢ (9500) 2100 (1:000)) (10000) 24000 22000 29 27 27 26 7000 (10000) 22000 (10000) 22000 (1500 26000 711000 24000 (12500) (11500) 26000 26 25 25 25 25000 23000 26000 28000 9000 (11000) (0500 (12509) P12000) (13500) (12500) 26 25 25 24 procal (12000. 27000 21500) 25000 (13500) 50000 (12000) 28000 (4500 32000 (13500) 30000 26 25 25 24 13009 (13500) 29000 (12000) 27000 (14500) 32000 (13500) 30000 26 26 FIGURE 2 (See appropriate aircraft flight manual for the correct information.)
B-737 1/4 INCH SLUSH OR STANDING WATER DEPTH
CROSS WEICHT REDUCTION LB FLAP POS PRESS ALT SI 4000 SL 2 4000 SL 4000 SI 10 4000 SI 10001 SL 25 4000 80 3400 3200 2300 3200 1800 3000 1600- 1500 22600 1500 2500 NORMAL LIMITED 100 90 3500 4500 4300 5400 3400 4500 4100 5100 3400 4500 3700 4900 4400 3300* 3000 4300 3900 4900 2800 4200 3900 4900 110 5700 6700 5500 6700 5200 5200 6200 5100 6100 4700 6100 WT 115 6100 7300 6100 7300
TICE BLUSH OR STANDING WATER DEPTH
CROSS WEIGHT REDUCTION LE FLAP POS 10 15 25 PRESS ALT :000 SL 4000 SL 4000 SL 4000 SL 4000 4000 80 6600 5300 6600 4800 6400 4500 6000 4300 5600 4200 5900 90 9000 7300 8600 7100 8400 6800 8400 6300 8300 6300 8300 9400 11200 9300 10900 9200 10700 9000 10400 9000 10400 9000 10400 110 12200 13900 12100 13500 12100 13400 12000 13200 12000 13000 12000 13000 115 13200 15000 13000 15000 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 runway condition on all-engine operating performance. (F.L. = field length) Par 4 Page 3
B-707 Slush Airport MAXIMUM CROSS WEIGHT AT BRAKE RELEASE FOR V1 = Vmcg - LB (KG) Runway Length Available 15 Depth Altitude 7,000 Ft. 8,000 Ft. 1,000 Ft. 11000 Ft.
1/4" Sea Level 144,000 3 500 (65,400) 0109,70 4000 Ft. 150,000 205,000 263,000 (68,000) (93,000) (119,200) 172,000 230,000 * * (78,000) (104,300) 4000 Ft 170,000 225,000 * (77,200) (102,000) FIGURE 4 (See appropriate aircraft flight manual for the correct information.)
* Not Vmcg Limited NOTE: See B-707 Operations Manual for V1 speed reductions.
B-147 LENGTH RUNWAY REDUCTION 25 IN (.64CM) SLUSH WEIGHT REDUCTION V1 REDUCTION 05 IN (1.3CM) WET CHT SLUSH REDUCTION REDUCTION WEIGHT ICE FAREDUEZICON
FT LB(KG) KTS LB( KG) KTS LB(KG) KTS 8000 9000 109000 (49,440) 47000 21,320 41 34 H,000 (32,66 73,000 (33,14 30 41 3-900 (68,490) 00 20,870 41 46 10000 47000 21,320 31 71,000(33,570) 27 25000(11,340) 36 47000 ,320. 30- 10,000 (35,380) 26 25000(11,340) 34 4700 28 18,000 (35,380) 25 25000 (11,340) 32 4700₴ •320 28 78,000 (35,380) 24 25000(11,340) 29 FIGURE 5 (See appropriate aircraft flight manual for the correct information.)
NOIF 1: In all applicable cases, V1 reductions are based on minimum Vi equal to Vmcg.
NOTE 2: Vmcg is based on actual ambient conditions.
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DC-10
EFFECT OF SLUSH/WATER ON BALANGED TAKEOFF PEPFORMANGE PRIMARY REVORSURS OPPRATIVE SIUSH OR WATER DEPTH = 1/4 INCH WEIGHT REDUCTION (1000 LB)
FLAP TAKEOFF FIELD LENCIH (FLET SETTING 6,000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 (DEG) 50 -22 -28 -34 -39 -43 =46 -50 -50 10° -24 -33 -39 →¾3 -45 45 15° -26 -35 -40 —45 →45 20° -30 -37 -42 -43 11 HODUCTION (KIAS
RUNWAY TAKEOFF FIELD LENGTH SLOPE 6,000 7,000 8,000 9,000 10,000 ,000 12,000 13,000 14,000 -22 -24, -25 -27 -28 -29 -30 -31 -24 -26 -27 -29 -31 -32 -33 -34 -1% -27 -29 -30 -32 -35 -36 →37 -39 SLUSH OR ATER DEPTH /2 INCI REDUCTION (1000 LB
FLAP FIELD LENGTH FEET SETTING 6,000 7,000 9,000 10,000 11,000 12,000 13,000 14,000 (DEG) -36 -52 -58 -62 —64 —64 -64 —64 -39 -56 -61 -62 -62 -62 -57 -60 -61 -61 →45 -58 -60 V1 REDUCTION (KIAS)
RUNWAY TAKEOFF FIELD LENGTH FEET SLOPE 000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 -19 -21 -26 -27 -27 -28 -19 -21 -23 -26 -28 -29 -30 -31 -1% -2 -23 -25 -27 -29 -31 -32 -34 -35 FIGURE 6 (See appropriate aircraft flight manual for the correct information.)
NOTE: The above performance information 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 manufacturers' operations/flightcrew operating manual for the specific model, engine power, and type aircraft operated.
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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 A tenarese J. A, FERRARESE Acting Director (light Standards Service Page 6 Par 4