How to get height above ground when over 5,000ft barometric?

May be a silly question, but I've often wondered, how do you get height above ground when altimeters only show barometric over 5,000ft?

Maybe you mistake the radar altimeter with the barometric one. Ehile the R altimeter is indeed limited, the barometric is not. The Radar altimeter is on the right console below the hook, the barometric one is near the standby airspeed indicator underneath the right DDI. Also, on the HUD control panel you can switch between baro and rad alt. When an R near the altitude display on the hud apperas, the radalt is displayed, otherwise it is the baro alt

Remember: the barometric altimeter is the one on which you can set the ambient pressure. The radar altimeter ia the onw on wgich you can set a warning height.

Ps: above a certain radalt, the hud always sgiws barometric altitude, regardless of the altimeter source switch

Thanks but I think you are misunderstanding my question.

I am asking how can you get height above ground when the barometric altitude is greater than 5,000ft.

I think ATC will give it to you. The carrier ATC will give it to you right before take off. Can't remember if you get it when requesting landing.

Thanks, but I'm thinking more of guaging bombing runs at altitude, in NTTR for example.

The radar altimeter will give you your AGL as long as it is less then 5000ft, no matter how high your barometric altitude is. You can fly at 20000ft baro, when the ground is at 17000ft you will still get the correct height AGL. If you are above 5000ft AGL you'll need a map and your baro alt to get your height above ground.

Sorry, I'm really not explaining myself well here!

What I mean is, how does one get a height AGL when it is more than 5,000ft? To plan a bomb attack for example.

Thanks, but I'm thinking more of guaging bombing runs at altitude, in NTTR for example.

RA is useless for a bombing run since you would need to know the altitude ahead of your airplane, not the altitude below the airplane.

What I mean is, how does one get a height AGL when it is more than 5,000ft?

You can't. You have to use a map.

RA is useless for a bombing run since you would need to know the altitude ahead of your airplane, not the altitude below the airplane.

I take your point, but I'm talking about a situation where there is relatively not much change in altitude between target point and current location. The altitude below the plane would give a reasonable guide to what you need to know. Whereas at the moment, you could be anything from 5001ft to infinity above the target! I know you've got your eyes, but still!

I guess the answer is 'you can't' as you already suggested!

I'm talking about a situation where there is relatively not much change in altitude between target point and current location.

If you need the approximate altitude (relatively not much change) baro altitude is precise enough.

May be a silly question, but I've often wondered, how do you get height above ground when altimeters only show barometric over 5,000ft?

Math.

Your altitude - ground elevation above MSL = AGL altitude.

What I mean is, how does one get a height AGL when it is more than 5,000ft? To plan a bomb attack for example.

You need to know target elevation, simple as that.

It's my understanding that attack pilots rarely engage targets of opportunity in uncharted territory. So, the targets could be preplanned, meaning the target elevation should be known down to a few feet precision. Or they could be assigned via some kind of controller, like JTAC or AFAC, who should include the target elevation in their briefing. And if you were to attack random targets of opportunity, a map might be a good way to gauge the general elevation of the target area to allow for a decent final attack. Once we get the TGP, I'm assuming it'll also show target elevation.

Now with target elevation known from any of the above sources, your height above target is obviously your altitude MSL minus target elevation, and that should be simple enough to do the math in your head.

Of course if someone insists on an altimeter setting that shows something other than QNH (altitude above MSL), the math might get a bit more complicated, so I would suggest setting QNH during fence in at the latest.

If you need the approximate altitude (relatively not much change) baro altitude is precise enough.

I don't think so!

Well, you simply don't a get a precise RA readout above the RA limit. Neither in DCS nor IRL.

Well, you simply don't a get a precise RA readout above the RA limit.

I'd say you don't get *any* RA readout above the RA limit :lol:

In real life your mission planning would be 1-2 hours on the ground going over all details of the target, ingress and exit routes. This would include the heights of the terrain over the route and in this case in the target area.

So if you want to bomb at 12,000 AGL, pre-flight you look at the target area and see it is 5,200 ft (for example) and know you are aiming to release at 17,200 ft baro.

I'd say you don't get *any* RA readout above the RA limit :lol:

I was trying to put the emphasis on the precision of the RA alt vs. baro alt.

You need to know target elevation, simple as that.

 

It's my understanding that attack pilots rarely engage targets of opportunity in uncharted territory. So, the targets could be preplanned, meaning the target elevation should be known down to a few feet precision. Or they could be assigned via some kind of controller, like JTAC or AFAC, who should include the target elevation in their briefing. And if you were to attack random targets of opportunity, a map might be a good way to gauge the general elevation of the target area to allow for a decent final attack. Once we get the TGP, I'm assuming it'll also show target elevation.

 

Now with target elevation known from any of the above sources, your height above target is obviously your altitude MSL minus target elevation, and that should be simple enough to do the math in your head.

 

Of course if someone insists on an altimeter setting that shows something other than QNH (altitude above MSL), the math might get a bit more complicated, so I would suggest setting QNH during fence in at the latest.

Thanks a lot, that is a really useful answer.

You see, baro altitude is precise enough ;)

I'm pretty sure the targeting pod will give you target elevation when it comes out

In general yes, you need to know target altitude and have an accurate baro altitude (this is clearly described in training docs for the T-45), however most aircraft have ways of obtaining an accurate height above target for bombing computation. In the Harrier it’s the DMT/ARBS, in the Hornet/Viper the A/G radar should be used (this can be used to range the ground at altitudes much higher than your RADALT). I’m curious if this is currently reflected in the Hornets CCIP accuracy as it should substitute the need to know an exact target elevation.

In general yes, you need to know target altitude and have an accurate baro altitude

On most airplanes (including the F/A-18 ) the baro altimeter has tolerance of +30ft and the stndby alt +60ft.

Hah, didn’t you just above say baro altitude is precise enough? But either way that’s exactly why modern strike aircraft have more accurate means of obtaining HOT, as I explained.