Technical Evaluation Engineering Aerodrome Safety, Civil Aviation - TP 13706

Order TP 13706E

January 1998

Table of contents

• Introduction
• Test Procedure
• Conclusions
• Recommendations
• Appendices
  • Appendix A - General Photographs
  • Appendix B - Test 1 to 27 Photographs
  • Appendix C - Test 28 to 40 Photographs
  • Appendix D - Test 41 to 54 Photographs
  • Appendix E - Test 55 to 68 Photographs
  • Appendix F - Test 69 to 83 Photographs
  • Appendix G - Test 84 to 99 Photographs

Introduction

Pursuant to a request from Transport Canada – Civil Aviation, a frost study was conducted on a number of designs of Precision Approach Path Indicator (PAPI) light units. The objective for the project is to eliminate the possibility of a false signal being presented to aircraft from a frosted PAPI, and thus to prevent a potential hazard. For more details, see terms of reference (Appendix "A").

The project is separated in 4 parts:

1. Determine the amount of operating time required to eliminate frost 1/16" (1.6 mm) from the PAPI lens or cover glass at different temperatures (-5, -10, -20, -30°C).
2. Determine the minimum current level for the PAPI lights to function with a partial frost accumulation on the lenses or cover glass at the same temperatures as in 1.
3. Determine the minimum current level for the PAPI lights to function without frost accumulation on the lenses or cover glass at the same temperatures as in 1.
4. Determine what is the effect of dew on PAPI signal at 0°C.

Test Procedure

Laboratory book for Precision Approach Path Indicator (PAPI)

Before the test:

1. We ensured that the test equipment conformed to standards (Check for ISO stamp).
2. We obtained the materials required to conduct the test procedures as stipulated in Canada Motor Vehicle Safety Standard, (CMVSS) 103. (paint gun, pressure regulator, Hydra, timer Cra-Lab, video camera, digital camera).
3. We installed a white 8' x 8' panel to receive the projected signal from the PAPI'S.
4. We installed the PAPI units on a table at the other end of the chamber (the PAPI projected the signal onto the panel surface). The supply current for the PAPI light unit was set at 6.6 Amp.
5. We adjusted the distance of the table so that the emitted light beam just covered the width of the target panel.
6. We lowered the temperature of the cold chamber to test temperature and confirmed this using a thermocouple measuring device.
7. A sign identifying the test being performed was prepared.

Defrosting:

Note: For this test, it was necessary to measure the thickness of the applied frost when sprayed with water. The adopted technique was to install a measured metallic disc between the two PAPI lenses, to create frost by spraying water vapor from a paint gun equally onto the entire front surface of the PAPI unit under test, including the metallic disc. After completing the application of water, the disc was removed and the total thickness of the disc plus frost was measured using a dial caliper. The thickness of the frost was measured as the difference between the total thickness and the thickness of the metallic disc.

1. A pre-test photograph was taken of the equipment under test.
2. A means to measure the thickness of the frost applied on the PAPI surface was installed (metallic disc between the lenses).
3. Vaporized water was sprayed onto the front of the PAPI unit (entire surface of optical window) to form a 1/16" thickness of frost (0.175 ml/cm2)
4. The application of vaporized water was video-taped and a still picture was taken after the application.
5. The metal measuring disc was removed and the total thickness of the disc plus the frost deposit was measured.
6. The thickness of the frost was calculated.
7. A 30 minutes time period was allowed to elapse to allow, for temperature stabilization as specified in CMVSS 103.
8. The video camera was started, the PAPI was turned on and operated at 6.6 Amperes while simultaneously starting a timer.
9. The end of the test was acknowledged as the moment when the signal displayed on the screen was identical to the signal displayed when the PAPI light unit was operating without any frost cover.
10. The time required for the PAPI defrosting to the point of producing a signal the same as a PAPI without frost cover was noted.
11. A post-test still photograph was taken.

Minimal current test:

1. A thermocouple was attached to the centre of one of the two PAPI lenses or at the beam centre point for PAPI equipped with a cover glass.
2. A pre-test still photograph was taken of the equipment under test and the test identification sign.
3. The PAPI light unit was operated at the specified current test level.
4. The test was delayed until there was a stabilization of the lens or cover glass temperature (approximately 1 hour).
5. The lens temperature was recorded.
6. An attempt was made to apply a thin coat of vaporized water onto the lens surface or onto the portion of the cover glass without the thermocouple. This procedure was video-taped.
7. A verification was made to see if the frost melted immediately from the lens or cover glass.
8. The test was considered successful if the frost melted and was eliminated. If this did not occur and permanent frost remained, the test was repeated by raising the current to the next required level.
9. A post-test still photograph was taken with the test identification sign.

Dew test:

1. The temperature of the cold chamber was lowered to 0 degrees Celsius. A panel was installed.
2. The PAPI units were installed at 12' of the surface measuring the light intensity.
3. A supplied current of one PAPI was set up at 6.6 Amp.
4. It was left in soak for 1 hour.
5. A photograph of the intact signal was taken.
6. With a kettle, vapor was generated under the glass/lens to form dew.
7. The brightness of the signal and the width of the bundle were compared and quantified approximately.
8. The test was video-taped.
9. A photograph of the signal with dew was taken.

Test report study of PAPI Frost/Dew

Test results

Dew test at 0°C

Defrosting time test at -5°C *

Notes: * Application of water did ice instead of frost.

Defrosting time test at -10°C

Defrosting time test at -20°C

Defrosting time test at -30°C

Minimum current test at -5°C

Minimum current test at -10°C

Minimum current test at -20°C

Minimum current test at -30°C

Defrosting test summary

Note: Each cell contains test #, defrosting time at 6.6 Amp. and comments.

Minimum current test summary (partly defrosted)

This table contains minimum current test results where the ice on the lens/cover glass begins to melt. (A donut shape of ice remains around the lens)

Note: Each cell contains test #, minimum current, lens temperature and comments.

Minimum current test summary (fully defrosted)

This table contains minimum current test results where the ice on the lens/cover glass completely melts.

Conclusions

Defrosting Tests:

Most of the PAPI took a longer time to defrost at -5°C and -10°C than at -20°C. This can be explained by the type of ice. At -5°C and -10°C, the ice is clear, at -20 °C, the ice is white.

The best average performance was achieved by Crouse-Hinds PAPI.

The best defrosting time was achieved by Siemens PAPI with wired cover glass at -20°C in 5 minutes.

The most energy efficient PAPI is the Crouse-Hinds.

Minimum Current Tests:

What was simulated during this test is a snow storm or ice storm depending on test temperature, on a PAPI already energized. We obtained three types of results: The ice is not melting at all, the lens defrosts partially or the lens defrosts instantly.

We did two summary tables (completely and partly defrosted) because even if the lense is partly defrosted, the signal can be considered complete based on our criteria. It is to be noted that even if we consider the signal to be complete during the tests at 12' from the receiving panel, it does not necessarily means that the signal will be complete in the "real world" (at 1 mile).

Only Crouse-Hinds PAPI can meet the completely clear lens requirement at every temperature that we tested.

Siemens and Cegelec PAPI can meet the completely defrosted lenses at temperature above -10°C. At temperature below -10°C, there is always ice remaining on the edges of the lenses.

For partly defrosted lenses, the minimum current vary from 5.5 Amps to 6.6 Amps at -30°C.

Recommendations

We recommend that other tests in the field be made to confirm the above conclusions which would also consider other parameters, such as the cooling effect of the wind, the effect of the sun on the observation of the output signal from distances greater than the 12 foot laboratory distance, the "real world" frost deposit thickness and deposit rate of, as well as other meterological conditions. We also need to establish a scientific way of calculating the degradation of the PAPI to what would be considered as a false signal, from a true signal.

Based on these tests results, the PAPI must be energized at least 53.5 minutes before any airplane landing or remain energized at 6.6 Amp at all time.