Introduction

• Installation variables have a real-world effect on the fixture’s Light Beam or the Field Photometrics.

• Disruption to the Photometric Beam effects the number of lights the pilot can see.

• This talk focuses on the part of the photometric beam that gets obstructed by the pavement and the effect on overall the pilots view of the lights.

“The secret of a good speech is to have a good beginning and a good ending; and to have the two as close together as possible” …. George Burns (No Relation To Burns Engineering)

Light Beam ObstructionElevation at Light Beam vs. Elevation at Fixture Edge

• FAA’s Elevation Tolerance is Measured From Fixture Edge to Low Side of the Pavement because of snow plow removal.

• From a photometrics point of view – we care about the elevation at fixture center (not edge) where the light beam is.

• On many projects, there exists a dispute between Contractors and Airport regarding elevation vs. photometrics.

Elevation vs. Photometric Angle

Beam Blockage

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Beam Blockage vs. Pilot’s Field of View(Good Visibility vs. Low Visibility)

Pilot’s point of view in good weather.

What About in Low Visibility?

Complicated Issue:

• Background Light: Daytime vs. Night-Time

• Type of Airplane – Cockpit Height.

• Light Fixture Photometric Intensity.

• Chromaticity.

• Others.

Past Research – Fog Chamber

Past Research

Fixtures Used: • R/W CTL was 5,000 candelas

• R/W TDZ was 7,500* candelas.

• R/W Edge was 20,000* candelas.

* Lower than current FAA values.

Number of Lights Pilot Sees at ThresholdEmpirical Data

Number of Lights Pilot Sees in Low Visibility

Effect Beam Blockage Has on Number of Lights Pilots Sees in Low Visibility

Cockpit Height

• Assumes that all lights have the same fixture elevation.

• Geometric, Linear Analysis only.

• Main Beam angles only.

Effect of Beam Blockage on Number of Lights in Low Visibility

Effect of Beam Blockage on Pilot’s View in Low Visibility

Variables Impacting Fixture Elevation at Light Beam

Transverse And

Longitudinal Tilt

Fixture Elevation at Low Side of Pavement

(FAA Req’t)

Tolerances of

Surrounding Pavement

Elevation of Fixture at Light Beam Exit To Adjacent

Pavement

Effect on Field Photometrics & Pilots Field of View

Design Percent

Grade

Can the Pilot See The Lights?

Pavement TolerancesGrade Tolerance > Electrical Tolerance

• Lateral: ± ¼” with 16’ Straightedge every 50’.• Corrective Actions only if 15% in a lot fail. Lot can cover

area of 20 R/W Ctl lights. • Similar criteria for Longitudinal• Not necessarily measured where the fixture is.

Possible Reasons: Pavement Specifications/Tolerances Pavement Tolerances

Grade Tolerance > Electrical Tolerance

FAA Spec < ¼”

Pavement Tolerances

Field Experiment:Field Experiment:

Measure the pavement slope next to the light fixture using a digital level.

The results showed that, in many instances, the slope around the can was 2.3% whereas theoretical was 1.5%

Pavement TolerancesField Experiment

ΣTolerances Effect On PhotometricsActual Example From Field

Item Tolerance Effect on Fixture Elevation at Light

Beam

Pavement Instead of 1.5% by design you have 2.3% slope next to

fixture.(Assumes low side is -1/16”)

0.138 inches

Transverse Tilt 1.0° 0.10 inches

Vertical Tilt 1.0° 0.05 inches

Fixture Height Below Grade at Light Beam = ~ 0.288 (< 3/8”)

Photometric Angle Blocked = ~ 3.2 °

Recommendations

1. Specify the Measurement Tool to be used by the Contractor to measure fixture elevation.

Recommendations

2. Perform 16’ Straight-edge Measurements for pavement tolerances at fixture locations.

3. Calculate Photometric Blockage for % Grades higher than 2.0%.

4. Specify and Inspect Base Can Level prior to pouring encasement.

5. Consider Photometrics in the Project.

The End?

Possible Reasons

Pavement Tolerances

Measuring Fixture Height:

- The actual height will vary greatly depending on the measuring tool used. Can easily vary by 3/8”

Possible Reasons

Analyze Snow Plow Removal Procedures/Equipment

Possible Reasons

Recommendation:Recommendation:

For new projects provide a detail to the Contractor or train the Contractor on the method to measure fixture elevation that most suites your Airport’s operational/snow plow removal constraints.

Possible Reasons: Pavement Specifications/Tolerances

Pavement Tolerances:Pavement Tolerances:

• Lateral: ± ¼” measured every 50’ w/ 12’ Straightedge. Not necessarily measured where the fixture is going to be located.

• Longitudinally: Measured with pfilograph. Cannot deviate by more than ½” on a single pass. ( A pass maybe ~ 500’)

• Correction Criteria: If 15% of the measurements in a lot than corrective actions shall be taken on the pavement. (On a recent overlay project a lot was 20’ wide by 900’ long or ~ 20 R/W CTL lights).

• At some Airports this is not aggressively regulated.

Possible Reasons: Pavement Specifications/Tolerances

Recommendation:Recommendation:

When performing the straightedge measurement of the pavement tolerances, survey the location of the lights and measure where the lights are going to be.

Possible Reasons: Base Can Tilt.

PavementCross Slope Point of measure

for HEIGHT tolerance

Light Base

Tilt from level

Pavement Grade(longitudinal) Measured Height

(low cross slope)

Light Base

Tilt from level

Level !!

TRANSVERSE SLOPE

LONGITUDINAL GRADEDeg Grade for 12”

for 6”

Ht Ht

1/2 0.9% 0.1” 0.05” 1 1.75% 0.2” 0.1”

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The End

Questions?Questions?