Stopping on Slippery Runways

Paul Giesman

Principal Engineer Flight Operations Engineering Boeing Commercial Airplanes

W029n.1

Landing on Wet/Slippery Runways

Landing • Information - Condition Reporting • Approach, Flare, and Touchdown • Stopping • Recommended Landing Procedure W029n.2

Information

Weather - winds, gust - approach speed Runway condition is typically provided three ways • PIREP’s (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.

W029n.3

Evaluation of information

• Flight crew needs to evaluate the information available to them – Time of report, possible changing conditions • Information may be conflicting – For example: – Braking action is good, runway description is slush covered – Measured friction is 0.35, runway description is slush covered – If runway is reported to have slush/standing water covering, the flight crew should be suspicious of braking action reports and measured friction W029n.4

Slush/Standing Water Report

• Hydroplaning(aquaplaning) is possible • Ground friction measuring vehicles are unreliable 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 W029n.5

Landing Performance Data Available to Crews (Boeing OM - Section PI)

Boeing performance data is provided for pilot 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 data labeled poor for slush/standing water due to the possibility of hydroplaning W029n.6

Sample OM

PI Slippery Runway Landing Data

Data provided for different braking actions and configurations Braking Configuration Max Manual Braking Autobrake Setting 2 Autobrake Setting 3 Max Autobrake Setting Sample data is from the 737 OM Reported Braking Action Dry Good Medium Poor Autobrakes are recommended on a slippery runway. • Medium, 3 or 4 are recommended depending on airplane W029n.7

Sample OM

PI Slippery Runway Landing Data

Sample data is from the 737 OM Adjustments for: • Weight • Altitude • Wind • Approach speed • Slope • Reverse thrust W029n.8

Sample OM

PI Slippery Runway Landing Data

*Note: JAROPS data includes a factor of 1.15

Sample data is from the 737 OM 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 W029n.9

Crosswind Guidelines

• Published in the Flight Crew Training Manual • Guidelines, not limitations Reference: Boeing Flight Crew Training Manual - 747-400 W029n.10

Landing on Wet/Slippery Runways

Landing • Information •

Approach, flare, and touchdown

•

Stopping

• Recommended landing procedure W029n.11

Landing

Approach, Flare, and Touchdown

Objective • Position the airplane on the runway at the target point at the minimum speed for the existing conditions. – Minimize the air distance – Maximize the stopping distance available • Factors that influence air distance – Flare technique – Approach speed – Approach path W029n.12

Landing

Approach, Flare, and Touchdown

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. Do not hold the nose wheel off the runway after touchdown.

• After main gear touchdown, begin to smoothly fly the nose wheel onto the runway by relaxing aft control column pressure. Reference: Boeing Flight Crew Training Manual W029n.13

10.0

8.0

Decel Kt/sec 6.0

4.0

2.0

0.0

Deceleration Rate Comparison

Air Versus Ground

Based on 747 at operational landing weight Wheel brakes, spoilers, and reverse thrust as noted

Dry Wet Icy Dry Wet Icy Dry Wet Icy 1/2"

Floating or Aerobraking No Reverse 2-Engine Reverse Thrust 4-Engine Reverse Thrust Note: On airplanes with more effective reversers the ratio of ground attitude deceleration can be 9-10 times more than floating deceleration.

W029n.14

Effect of “Floating”

Normal VTD + 10 20 15 Excess approach speed knots 10 5 Normal VTD Normal VTD - 10 0 0 1,000 2,000 3,000 4,000 Increase in air distance - feet 5,000 6,000 Excess speed: • 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 W029n.15

Excess Speed at Touchdown Effects Stopping Distance

• Greater touchdown velocity causes longer ground distance Same weight, same runway conditions VTD Stop VTD + 10 Stop W029n.16

Landing Distance Increase due to Excess Touchdown Speed

Medium 20 Dry Good, wet 15 Excess touchdown speed, kt 10 5 Poor, wet ice / hydroplane 0 0 200 400 600 800 Increase in stopping distance, ft 1,000 1,200 Based on 747 at operational landing weight - 4-engine reverse thrust W029n.17

Excess Threshold Height

Excess Height Normal 50 ft Increased in Distance to Touchdown Excess height at threshold, ft 80 60 40 20 Based on a 3-degree glideslope 0 0 500 1,000 1,500 Increased in distance to touchdown, ft W029n.18

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 W029n.19

Runway Friction Capability

Hydroplaning •

Viscous

- normal wet runway friction •

Dynamic

“planing” of the tire on standing water and slush •

Reverted rubber

- locked wheel hydroplaning W029n.20

Viscous Hydroplaning

Normal Wet Runway Friction

Thin film of water acts like a lubricant. The microtexture (sandpaper type roughness) of the runway surface breaks up the water film and greatly improves traction. Dry runway Airplane braking coefficient Rougher microtexture Smoother microtexture Ground speed, kt W029n.21

Airplane braking coefficient

Dynamic Hydroplaning

Commonly Called “Hydroplaning”, “Aquaplaning”

At high speeds the tire “planes” on deep slush/standing water. Tire grooves and macrotexture (stony or grooved surface) help drain water from the footprint and improve traction. Dry runway V HP = 8.63

Tire pressure, psi .9V

HP V HP Ground speed, kt Nil braking above 90% of dynamic hydroplaning speed W029n.22

Reverted Rubber Hydroplaning

Locked Wheel

Steam Steam

When a tire locks up on a smooth wet 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.

Reverted rubber hydroplaning is not an issue on post-1980 airplane designs due the improvement in anti-skid system hydroplane protection.

W029n.23

Effect of Runway Condition on Stopping Distance

160 140 120 100 Ground speed, kt 80 60 Dry Wet, good Medium Poor, wet ice / hydroplane 40 20 0 0 1,000 2,000 3,000 4,000 5,000 Distance to stop, ft 6,000 Based on 747 at operational landing weight - Wheel brakes, spoilers, 4-engine reverse thrust 7,000 8,000 W029n.24

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 due to wheel brakes Effect of ground spoilers Reverse thrust Aero drag Wheel brakes Ground spoilers

49000 54000 168000

No ground spoilers

49000 35000 106000

0 0 100,000 200,000 Stopping force, lb Based on 747 at operational landing weight - Wheel brakes, spoilers, 4-engine reverse thrust, 120 knots 300,000 W029n.25

Effect of Spoilers

Total stopping force, lb = Reverse thrust + aero drag + wheel brake Dry Good Medium Poor Spoilers deployed 270,100 194,400 148,500 125,600 Spoilers stowed 190,400 142,300 113,200 98,600 Spoiler effect % stopping force 29 % 27 % 24 % 21 % Based on 747 at operational landing weight - Wheel brakes, spoilers, 4-engine reverse thrust - 120 knots W029n.26

Effectiveness of Stopping Devices

• Slippery runway - thrust reverser and aerodynamic drag become dominate stopping force as runway slipperiness increases Percentage of Reverse thrust Aero drag Wheel brakes stopping force due to drag and reverse thrust Poor - wet ice/ 80 % hydroplaning Medium 70 % Good, wet 55 % Dry 0 100,000 200,000 Stopping force, lb Based on 747 at operational landing weight - Wheel brakes, spoilers, 4-engine reverse thrust - 120 knots 300,000 35 % W029n.27

Automatic Braking

Boeing recommends autobrake when landing 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 W029n.28

V Ref V Ref V Ref

AFM Landing distance

Stop

Demonstrated dry capability

Stop 1.67 factor

FAR dry

Stop 1.67 factor 1.15 wet factor

FAR wet

W029n.29

V Ref

Distance Comparison “

Book” Data

Stop 1.67 factor 100 % 1.15 wet AFM - FAR wet Stop

70 %

Stop

90 %

OM - Max manual OM - A/B 3 “Good” Stop

90 %

OM - A/B 3 “Medium” Stop OM - A/B 3

110 %

OM - Max manual Based on 747 at operational landing weight - OM data based on unfactored, 4-engine reverse thrust assuming a 1,200-ft touchdown point.

“Poor” W029n.30

Distance Comparison

50-ft High and Extended Flare (Floating)

V Ref 100 % Stop 1.67 factor 1.15 wet V ref+ 10 1200 ft VTD normal 1200 ft V ref+ 10 VTD normal Stop AFM - FAR wet

100 %

Stop Max Manual

120 %

A/B 3 1200 ft V ref+ 10 VTD normal Stop

120 %

A/B 3 “Good” “Medium” 1200 ft V ref+ 10 VTD normal Stop

140 %

A/B 3 Max Manual Based on 747 at operational landing weight - 4-engine reverse thrust - extended flare data is based on a 10-kt high approach speed bled off during the flare maneuver.

“Poor” W029n.31

V Ref

Distance Comparison

50-ft High and Extended Flare (Floating) Plus No Reverse Thrust

Stop 1.67 factor 100 % 1.15 wet AFM - FAR wet V ref+ 10 1200 ft VTD normal 1200 ft V ref+ 10 VTD normal Stop

110 %

Max Manual Stop

130 %

A/B 3 “Good” 1200 ft V ref+ 10 VTD normal Stop

140 %

“Medium” A/B 3 1200 ft V ref+ 10 VTD normal Stop “Poor”

180 %

A/B 3 Max Manual Based on 747 at operational landing weight - 4-engine reverse thrust - extended flare data is based on a 10-kt high approach speed bled off during the flare maneuver.

W029n.32

Summary

Recommended Procedures

Information • Evaluate all the information before the approach – Wind, weather, runway condition, etc.

– If runway conditions warrant, review the performance data to ensure the runway length exceeds the expected stopping distance by an adequate margin W029n.33

Summary

Recommended Procedures (continued)

• Prepare to land the aircraft – In the touchdown zone – 1,000-ft 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 W029n.34

Summary

Recommended Procedures (continued)

• 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 W029n.35

Summary

Recommended Procedures (continued)

• Raise spoilers as soon as possible after touchdown (confirm auto spoiler deployment) – Increase load on the gear • Initiate braking once spoilers have been raised and nose wheels have contacted the runway – Apply brakes smooth and symmetrically W029n.36

Summary

Recommended Procedures (continued)

• Initiate reverse thrust as soon as possible after touchdown • Target the rollout to stop well short of the end of the runway – Leave margin for unexpectedly low friction due to wet rubber deposits or hydroplaning W029n.37