# Presentation: 313803

## 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 ObstructionElevation at Light Beam vs. Elevation at Fixture Edge

- _Light Beam Obstruction_Elevation 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 ThresholdEmpirical Data 

## 

## Number of Lights Pilot Sees in Low Visibility

- __

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

-   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 TolerancesGrade Tolerance > Electrical Tolerance 

- Lateral: ± 1⁄4” 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 < 1⁄4”

## Pavement Tolerances 

- _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 Tolerances_Field Experiment

## ΣTolerances Effect On PhotometricsActual 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

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

## Recommendations

- Perform 16’ Straight-edge Measurements for pavement tolerances at fixture locations.
- Calculate Photometric Blockage for % Grades higher than 2.0%.
- Specify and Inspect Base Can Level prior to pouring encasement.
- 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:_
- 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:_
-   Lateral: ± 1⁄4” 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 1⁄2” 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:_
- 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.  

**Level !!**

**TRANSVERSE SLOPE**

**LONGITUDINAL GRADE**

## The End 

- _Questions?_