Stopping on Wet and Slippery

8/3/2019 Stopping on Wet and Slippery

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Flight Operations Safety

Stopping on Slippery Runways

Captain David C. Carbaugh

Captain Glenn C. Spakes


Boeing Commercial Airplanes


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Landing on Wet/Slippery Runways

Landing

Information - Condition Reporting

Approach, Flare and Touchdown

Stopping

Recommended Landing Procedure


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Information

Weather - Winds, gust - Approach Speed

Runway condition is typically providedthree ways

PIREPs (pilot reports) - braking action - good,fair, medium, poor, nil

Description of runway condition

Snow, wet, slush, standing water, sand treated

compact snow etc. Reported Friction based on Ground Friction

Vehicle report

30 or 0.30 etc.


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Evaluation of information

Flight crew needs to evaluate all theinformation available to them

Information may be conflicting

For example

Braking action is good, runway description is slushcovered

Measured friction is 0.35, runway description is slushcovered

If runway is reported to have slush/standing watercovering, the flight crew should be suspicious ofbraking action reports and measured friction


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Slush/Standing Water Report

Hydroplaning(aquaplaning) is possible

Ground friction measuring vehicles areunreliable when the runway is covered with a

depth of contaminant that exceeds*: Water -1 mm

Slush/wet snow -3 mm

Snow- 2.5 cm

*Reference - FAA AC 150.5200-30A


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Landing Performance Data Availableto Crews (Boeing OM - Section PI)

Boeing performance data is provided forpilot decision making

Information published as a function of

Reported Braking Action Good - Wet runway, JAR defined compact snow

Medium - ice, not melting

Poor - Wet melting ice

For landing, Boeing recommends the use of the datalabeled poor for slush/standing water due to thepossibility of hydroplaning


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Sample OM - PI Slippery Runway LandingData

Data provided for

different Braking

Actions and

Configurations

Reported Braking Action

Dry Good Medium Poor

Braking Configuration

Max Manual Braking

Autobrake Setting 2

Autobrake Setting 3

Max Autobrake Setting

Autobrakes are recommended

on a slippery runwayMed, 3 or 4 are recommended

depending on airplane

Sample data is from the 737 OM


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Adjustments for:

Weight

Altitude

WindApproach Speed

Slope

Reverse Thrust

Sample data is from the 737 OM


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Actual (unfactored*) distances are shown

Based on flaps 40, VREF40 approach speed

Landing distance required includes 1000 ft of air distance

1200 for 747

Includes 2 engine reverse thrust*Note: JAROPS data

includes a factor of 1.15Sample data is from the 737 OM


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Flight Operations SafetyCrosswind Guidelines

Reference: Boeing Flight Crew Training Manual - 747-400

Published in theFlight Crew Training Manual

Guidelines - not limitations


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Landing on Wet/Slippery Runways

Landing

Information

Approach, Flare and Touchdown

Stopping

Recommended Landing Procedure


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Landing -Approach, Flare andTouchdown

Objective Position the airplane on the runway at the target

point at the minimum speed for the existingconditions.

Minimize the air distance

Maximize the stopping distance available

Factors that influence air distance

Flare technique

Approach speed Approach path


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Landing -Approach, Flare andTouchdown

Land in touchdown zone Do not allow the airplane to float. Fly the airplane onto the

runway and accomplish the stopping procedure.

Do not attempt achieve a perfectly smooth touchdown. Donot hold the nose wheel off the runway after touchdown.

After main gear touchdown, begin to smoothly fly the nosewheel onto the runway by relaxing aft control columnpressure.

Reference: Boeing Flight Crew Training Manual

D l ti R t C i


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Deceleration Rate ComparisonAir vs. Ground

Based on 747 at operational landing weight

Note: on airplanes with more effective reversers the ratio of ground

attitude deceleration can be 9-10 times more than floating deceleration

DecelKt/sec

Dry

Wet

1/2"

Icy

Dry

Wet

Icy

Dry

8.0

6.04.0

2.0

0.0

Floating orAerobraking

No Reverse 2 EngineReverseThrust

Wet

Icy

4 EngineReverseThrust


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Excess speed

Effect of "Floating"

0

5

10

15

20

0 1000 2000 3000 4000 5000 6000

Increase in Air Distance

Exc

essApproach

Speed

Normal VTD + 10

Normal VTD

Normal VTD - 10

Bleeding off excess speed during flare will increase air distance by:150 to 200 feet / knot of speed reduction

225 to 275 feet / second of additional air time

Based on 747 at operational landing weight - 4 thrust reverser


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Greater touchdown velocity causes longerground distance

Excess speed at touchdowneffects stopping distance

Same weight, same runway conditions

VTD

VTD + 10

Stop

Stop


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Landing Distance Increase due to Excess

Touchdown Speed

0

5

10

15

20

0 200 400 600 800 1000 1200

Dry

Good - Wet

Poor - Wet Ice / Hydroplane

Medium

Excess

Touchdown

Speed- Knots

Increase in Stopping Distance - Feet

Based on 747 at operational landing weight - 4 engine reverse thrust


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Excess Threshold Height

ExcessHeight

Increased in Distance

to Touchdown

0

20

40

60

80

0 500 1000 1500

Increased in Distance to Touchdown - Feet

Excess Height

@ Threshold

(Feet)

Based on a

3 degree glideslope

Normal 50 feet


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Landing -Stopping / Roll out

Objective Stop the airplane within the remaining runway available.

Factors affecting stopping distance

Reduced runway friction capability Wet

Standing Water / Slush

Ice / compact snow

Effectiveness of stopping devices

Thrust reversers, ground spoilers, wheel brakes


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Runway Friction Capability

Hydroplaning

Viscous - normal wet runway friction

Dynamic - planing of the tire on standing water

and slush Reverted rubber - locked wheel hydroplaning

Vi H d l i


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Viscous Hydroplaning- Normal wet runway friction

Thin film of water acts like alubricant. The microtexture

(sandpaper type roughness) of the

runway surface breaks up the water

film and greatly improves traction.

Airplane

Braking

Coefficient

Ground Speed - knots

Dry runway

Rougher microtexture

Smoother microtexture

D i H d l i


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Dynamic Hydroplaning- Commonly called hydroplaning, aquaplaning

At high speeds the tire planes on deepslush/standing water. Tire grooves and

macrotexture (stony or grooved surface)

help drain water from the footprint and

improve traction.

Airplane

Braking

Coefficient

Ground Speed - knots

Dry runway

Nil braking above 90% of

dynamic hydroplaning speed

VHP

VHP

= 8.63 Tire Pressure - psi

.9VHP

R t d R bb H d l i


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Reverted Rubber Hydroplaning- Locked wheel

When a tire locks up on a smoothwet or ice surface, the friction heat

generates steam. The steam pressure

then lifts the tire off the runway, and

the steam heat reverts the rubber to a

black gummy deposit.

SteamSteam

Reverted rubber hydroplaning is not an

issue on post-1980 airplane designs due

the improvement in anti-skid systemhydroplane protection.

Eff t f diti


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Ground

Speed- knots

0

20

40

60

80

100

120

140

160

0 1000 2000 3000 4000 5000 6000 7000 8000

Poor - Wet Ice

Hydroplane

Dry

Wet - Good

Medium

Effect of runway condition onstopping distance

Distance to Stop - feetBased on 747 at operational landing weight - 4 engine reverse thrust


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Effectiveness of Stopping Devices

Dry runway - Wheel brakes are the most effective

stopping devices Lift reduction due to spoiler deployment contributes

greatly to the generation of effective stopping force dueto wheel brakes

Based on 747 at operational landing weight - 4 engine reverse thrust - 120 knots

Effect of Ground Spoilers

Ground Spoilers

No Ground Spoilers

0 100,000 200,000 300,000

Stopping Force - lbs

49000

49000

54000

35000

168000

106000

Reverse

Thrust Aero

Drag

Wheel

Brakes


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Effect of spoilers

Total Stopping Force - (lbs ) = Reverse Thrust + Aero Drag + Wheel BrakeSpoiler Effect

Spoilers Deployed Spoilers Stowed % Stopping Force

Dry 270,100 190,400 29 %

Good 194,400 142,300 27 %

Medium 148,500 113,200 24 %

Poor 125,600 98,600 21 %



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0 100000 200000 300000

1

2

3

4

Stopping Force - lbs

Slippery runway - Thrust reverser and aerodynamic

drag become dominate stopping force as runway

slipperiness increases

Effectiveness of Stopping Devices


% of stopping

force which is

drag and reverse

thrust

80 %

70 %

55 %

35 %

Poor - Wet Ice/Hydroplaning

Medium

Good - Wet

Dry

Reverse

Thrust

Aero

Drag

Wheel

Brakes

0 100,000 200,000 300,000


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Automatic Braking

Boeing recommends autobrake whenlanding on a slippery runway

Setting 3 or 4 for wet or slippery runway

Actual setting dependent on model Autobrake assures prompt application of the

brakes after touchdown

Autobrake performance capability is limited by

the runway friction capability


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AFM Landing distance

VRef

Stop

Stop1.67 factor

Stop1.67 factor 1.15 wet

factor

Demonstrated Dry Capability

FAR Dry

FAR Wet

VRef

VRef


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Distance Comparison - Book Data

Stop1.67 factor 1.15

wet AFM - FAR Wet

VRef100 %

Stop OM - Max Manual

Stop

70 %

90 %OM - A/B 3

Stop 90 % OM - A/B 3

Good}

OM - Max Manual

OM - A/B 3Stop

110 % Poor}

Medium}

Based on 747 at operational landing weight - OM data based on unfactored, 4 engine reverse thrust

assuming a 1200 foot touchdown point.

Distance Comparison 50 Feet


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Distance Comparison - 50 FeetHigh and Extended Flare (floating)


wet AFM - FAR Wet

VRef

100 %

Stop Max Manual

Stop

100 %

120 % A/B 3

Good

}

Max Manual

A/B 3Stop

140 %Poor}

Medium}

Based on 747 at operational landing weight - 4 engine reverse thrust - extended flare data is based

on a 10 knot high approach speed bled off during the flare manuever.

Vref+ 10VTD Normal

Stop 120 % A/B 3

Vref+ 10VTD Normal

Vref+ 10VTD Normal

Vref+ 10VTD Normal

100 ft

100 ft

100 ft

100 ft

Distance Comparison 50 feet high and


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Distance Comparison - 50 feet high andextended flare (floating) plus No Reverse Thrust


wet AFM - FAR Wet

VRef

100 %

StopMax Manual

Stop

110 %

130 % A/B 3

Good

A/B 3Stop

180 %

Poor

Medium

Vref+ 10

VTD Normal

Stop 140 % A/B 3

Vref+ 10VTD Normal

Vref+ 10VTD Normal

Vref+ 10VTD Normal

100 ft

100 ft

100 ft

100 ft

Based on 747 at operational landing weight - 4 engine reverse thrust - extended flare data is based

on a 10 knot high approach speed bled off during the flare maneuver.

}

Max Manual

Summary:


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Summary:Recommended Procedures

Information

Evaluate all the information available beforethe approach

Wind, weather, runway condition etc. If runway conditions warrant, review the performance

data to ensure the runway length exceeds theexpected stopping distance by an adequate margin

Summary:


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Prepare to land the aircraft In the touchdown zone 1000 feet target

On centerline

With minimal lateral drift Without excess speed

Normal speed additives

Arm auto spoilers and auto brakes as

appropriate Assures prompt stopping effort after

touchdown

Summary:


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Flare and Touchdown

Flare should lead to a firm touchdown

Extended flare will extend touchdown

and delay braking Lower the nose as soon as main

gear touches down

Increases load on the gear

Summary:


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Raise spoilers as soon as possible aftertouchdown (confirm auto spoilerdeployment)

Increase load on the gear

Initiate braking once spoilers have beenraised and nose wheels have contacted therunway

Apply brakes smooth and symmetrically

Summary:


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Initiate reverse thrust as soon as possibleafter touchdown

Target the rollout to stop well short of theend of the runway

Leave margin for unexpectedly low friction dueto wet rubber deposits or hydroplaning

Documents

Stopping on Wet and Slippery