VGSI

Question 1

To what degree above obstacles, left and right of course, and to what distance to VGSIs provide guidance?

Answer 1

VGSI’s are aligned
to provide a glidepath not less than 1.0⁰ above obstacles, 10⁰ either side of the
runway centerline, to a distance of 3-5 miles.

Question 2

What TCH do VGSIs provide?

Answer 2

They provide a TCH between 23-75 feet. The largest aircraft that normally operate on the runway determines the threshold crossing height.

Question 3

How are VASIs numbered?

Answer 3

Numbering for boxes starts at the runway. Numbering of the rows starts at the threshold. The number after the name is the total number of boxes that make up the system. Numbering is reversed ICAO.

Question 4

To what distance can a VASI-2 be used?

Answer 4

3 miles.

Question 5

To what distance can a SAVASI-2 be used?

Answer 5

1.5 miles

Question 6

To what distance can a VASI-4 be used?

Answer 6

4 miles

Question 7

To what distance can a Walker 3-Bar Vasi-6 be used?

Answer 7

3 miles

Question 8

What is the purpose of the far bar in a Walker 3-Bar Vasi?

Answer 8

The far bar and the middle bar provide
an additional glidepath slightly steeper
than the one provided by the near bar
and middle bar.

Question 9

To what distance can a VASI-12 be used?

Answer 9

5 miles

Question 10

To what distance can a VASI-8 be used?

Answer 10

5 miles

Question 11

For what type of aircraft are Walker 3-Bar VASI-16s intended?

Answer 11

Large, good for 5 miles.

Question 12

How many lights do PAPIs have?

Answer 12

2 or 4

Question 13

To what distance can a 4-box PAPI system be used?

Answer 13

4 miles

Question 14

To what distance can a 2-box PAPI system be used?

Answer 14

2 miles

Question 15

To what distance can a PVASI be used?

Answer 15

4 miles

Question 16

What are the colors of a TRI-Color Vasi (TRCV) and what do they represent?

Answer 16

Amber, above path; Green, on path; Red, Below Path

Question 17

When is a commissioning inspection required for VGSI systems?

Answer 17

• A commissioning inspection is required for all new VGSI(s) with an associated IFR procedure (to include circling approaches).
• Many existing VGSI(s) were placed into service without flight inspection: they may remain in service without a commissioning-type inspection until reconfigured to new
systems or the addition of electronic vertical guidance to that runway.

Question 18

Do VGSI require a periodic inspection?

Answer 18

No, there is no requirement, however surveillance of safe operation is accomplished in conjunction with other inspections on the associated runway.

Question 19

What is the tolerance for light intensity?

Answer 19

Ensure all lamps are operating and are at the same relative intensity for each setting.

Question 20

What is the angle tolerance for VGSIs?

Answer 20

3.0 +/- .2 unless a higher angle is necessary for obstacle clearance. The angle must be published in the AFD. The visual and electronic glidepath should be the same from between 6000-1000 ft prior to the threshold.

Question 21

How do we measure PAPIs using the on-path method?

Answer 21

Measure the aiming angle of the individual light boxes. It will be box 2 and 3 for a 4-box system and box 1 and 2 for a 2-box system. Do this by slightly ascending and descending through one light box changing from red to white and white to red. Mark the light change when it turns pink. AFIS measures the actual aiming angle of that light box, which should be
done an equal amount of times on top and bottom.
• Once the angles of the 2 boxes are determined, average them together to get the actual glidepath angle of the system.

Question 22

How do we measure lights on the level run method and how many runs are required?

Answer 22

Mark AFIS for each red-to-white transition (waypoint mark) and average the results of 2 runs.

Question 23

How do we measure coverage on VGSI systems?

Answer 23

Fly at a 90 degree angle to runway centerline using an altitude that allows the lights to be easily seen while remaining safely above obstacles. For lights installed on one side of the runway, all must be visible throughout the 20 degree coverage area, for installations on both sides of the runway, coverage on one side is acceptable.

Question 24

What should an inspector do if guidance is not provided 10 degrees either side of centerline?

Answer 24

The facility must be notamed and you should ensure that the information gets updated in the AFD.

Question 25

How is obstruction clearance measured on VGSIs?

Answer 25

Make 3 approaches, one on centerline, and on 10 degrees either side of centerline, a definite climb indication must be showing while maintaining clearance above all obstacles. The visual glidepath will be at least 1.0 degree above all obstacles.

Question 26

Should Baro VNAV be used to check glidepath coincidence with VGSI?

Answer 26

No, instead mathematically check published path angle of approach procedure against VGSI angle. LPV/GLS may be used because they define a fixed path that does not vary with temperature.

Question 27

What is the design tolerance for angle and TCH for coincident VGSIs and IAPs?

Answer 27

.2 degrees and 3 feet

Question 28

To what distance will the flight inspector evaluate obstacle penetrations?

Answer 28

8 nm. This distance my be reduced to 4 nm for 2-box PAPIs and other low intensity or non-standard systems with limited visibility.

Question 29

While on the VGSI glidepath, you must make sure there is no interference and it’s easy to identify what the lights are indicating (System Identification/Contrast), what should you do if there is any question of misidentfication or interference?

Answer 29

You should check the system at night.