JTAC 9-line altitude

[mmusson]

When an altitude is given by JTAC I believe it is it feet above sea level.

 

The plane's altitude reading is based on the current barometric pressure setting. The plane's pressure setting would be set to the take off location. Or possibly a standard value such as 29.92?

 

Won't this give a big enough error for low altitudes that it isn't useful?

[Brit_Radar_Dude]

For those reading this thread who are bemused by the term 9-line, it is a standardised briefing from an Air Controller (either on the ground or airborne) to an attack aircraft.

Contains the following information,

1. Initial point (IP). A known position on the ground.

2. Heading from the IP to the target.

3. Distance from the IP to the target in nautical miles.

4. Target elevation in feet above mean sea level.

5. Target description.

6. Target location coordinates.

7. Type of marker, smoke, laser, etc.

8. Location of friendlies from the target - direction and distance.

9. Egress direction and/or control point after attack.

 

To answer mmusons question:- The altitude in a 9-line is the true altitude of the target. Usually taken off a map.

 

I'm in the middle of re-reading my copy of A-10s over Kosovo and in Chapter 7 it talks about an AFAC using the contour lines on a 1:50,000 map to figure out the targets elevation before he passed the 9-line to the aircraft he was controlling.

 

Why does the attack pilot need the target elevation? One reason is the weapon release height. Cluster weapons for example are affected by release height. Too high and the submunitions spread over too wide an area and the P(k) is reduced and some targets may not be hit. Too low and they don't spead out enough.

Some types of cluster submunition may not have time to arm themselves if the release altitude of the cluster bomb is too low. Some types of submunition are prone to failure if the angle of impact is too great.