What's going on in this picture

Sorry guys, I posted this right before a flight from Tokyo to LA. Then I've been checking the posts occasionally. I wonder if you check in on your ipad if it shows you logged in everytime you use safari? I've also been busy the last few days flying this....
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Anyways, the correct altimeter for that altitude is 29.92. However, in the 747 it says STD or "standard" when you set 29.92 (a button push). The 29.94 is the preset for our approach. 29.94 was the local altimeter setting in Narita when we approached. When we cross transition level, we just push the button and the preset becomes the active. It's true different countries have different transition levels. I believe they are based on the highest terrain in the country. In Japan, it's 14,000. Hong Kong, 11000. Anyways, the altimeter isn't what's unusual.

 

What is a little strange is that while we are at FL360 (36000 for non flyers), our radio altimeter shows 1140. I realize most GA aircraft don't have radio altimeters. So I figured most of you wouldn't know what that 1140 meant. The RADIO 200 in green above it sorta gives away the fact thats radio altitude. For those non flyers, radio altitude is the altitude above the ground, not sea level.

So what gives? We are at 36000 ft but only 1140 feet above the ground? How's that possible??

Sorry for the confusion earlier in this thread. I guess I didn't post the question very well.

 

There was a plane underneath you? That would be something

 

I would have never guessed the radar altimeter, our radar altimeter is a stand alone instrument.

I'm sure our radar altimeters are a few generations older than what is used on the 747 but here is my guess. It's not all that uncommon for us to get wacky radar altimeter numbers, they usually attribute it to dirt from landing on assault strips on the bottom of the aircraft and the solution is to just clean off a little panel on the bottom of the aircraft. Maybe you had some crap on the bottom of the plane that caused some faulty indications up at altitude.

 

I thought that was what it was!

The question is, why? It's not a preset, since you have that set to 200. Can you set the altitude where the radar altimeter comes on?

I used to fly a Learjet where the radar altimeter would randomly come on at altitude-- a glitch. Sometimes the DH light going on and off would be annoying enough that we would pull the circuit breaker.

 

Edit: remove potential spoiler.

All the best,
Andrew.

 

Just thought of something else...do you have an altimeter test? When you preflight ours you press the test button and it goes to 500' then 300' which causes the "low" light to illuminate then 0'. If you press the test button in flight it causes the test sequence to go through it's motions but then it will go back to whatever altitude you are actually it. If you have a new guy you wanna screw with you can press the test button rapidly over and over in flight which will cause the indicator to gyrate wildly around with brief stops at the aforementioned altitudes confusing the hell out of the new guy. It's pretty funny really.

Another favorite trick is to "run out" of liquid oxygen. Normally maintenance keeps it around 20 liters but minimum LOX is 5 liters and they gotta bring in special equipment to purge the system if it gets below 2.5 liters which is a huge pain in the ass if you are on the road someplace. Usually running out of LOX is cause somebody left their quick don mask in emergency while preflighting. So if you are on the road and wanna screw with a new guy you turn off the LOX valve at the tank (so you don't actually drain it down) then set the new guys quick don mask to emergency. Push the test button so the gauge goes to zero then pull the circuit breaker. Then "somebody notices" that the plane is out of LOX and can't fly anywhere, gonna have to fly in a LOX cart. Ok, fess up, who left their quick don in emergency? You are gonna be the one to call the commander and explain why we are stuck here overnight, boy is he gonna be mad. Build it up for a bit until the victim is ready to call and confess.

Maybe the airline guys don't play ass hole tricks on each other.....

 

Interesting stuff.... I have heard of similar things in the C-130 world and it will usually get you is some serious trouble. No radar altimeter means no GCAS and other stuff and it's typically very bad juju to disable that sort of equipment on purpose.

 

Lou- What is the maximum height for radar altimeter readings in a 747-8? Most have an altitude above which they will not lock on.

On the altimeter setting, STD means 29.92 and 29.94 is the last local altimeter setting? Does the altimeter automatically go to 29.92 at FL 180 or do you have to set it? In the UK there are flight levels below FL180.

 

The radio (radar) altimeter comes alive at 2500 ft. So that's the maximum height.

The altimeter won't automatically switch from local to Standard or vice versa. The display will turn amber when passing the transition level/altitude reminding you to change it. This is based on FMS information.

I'd i remember correctly, Fiji has a transition level of 3000 ft. That's the lowest I've seen.

 

That's it! Sometimes as you pass a plane 1000 ft below you you'll get a quick 1000 ft flash on the radio altimeter. In this case, we were both flying the same direction over the Pacific towards Asia. So he was down there for awhile. That inspired the picture and the post.

In RVSM airspace, the separation is 1000 ft. So typically the other plane is coming at you 1000 ft above or below. But on one way airways or over the oceans, you'll get traffic the same direction at 1000 ft.

So for all those that guessed another plane caused the 1140 radio altimeter display, well done!

Sorry for the altimeter confusion. I should have blanked the preset.

Lou

 

Could this "false" information prove deadly in flight under the right circumstances?

 

Due to a case I'm working on, I know way, way too much about the C130's GCAS, TAWS, and RADALT system on the. Block 6.0/6.1 update. Fun stuff.


Mark

 

Wow, would have never guessed that you would get a radar altimeter return from another aircraft.

MAFFS 7?

 

That was my immediate guess, seen it many times. It's something that people in my community tend to forget. There was about a two year stretch where I was flying 3-4 times a week but never got above 6k feet.

 

Royal Norwegian Air Force.



Mark

 

I saw that and thought that the answer was that you had a momentary radio altimeter readout with the top of another airplane at 350 RVSm flying directly under you - although timing the picture to that momentary flash (he would be going in the opposite way of course) would have been incredibly hard even with an extremely quick shutter speed. And where are the lines in the EADI if you got the picture off? My guess is radio altimeter gremlins.

Edit: read the posts further and saw you were flying the same direction. Forgot about PAC routes...my bad

 

IN RVSM alt, wouldn't traffic at same direction show a 2000' delta, and not a 1000' as stated? I think opposite dir traffic will show a 1000' delta, but that would put closing traffic on the same alt block. hmmmmmmm

 

You want to push the CB in before you descend below FL180, although in the Learjet (at least most of them), the radar altimeter doesn't have a lot of ancillary functions. It would have disabled the old GPWS, but TAWS or EGPWS doesn't use it.

And, at night, the DH light is very bright and quite annoying for a few hours.

 

Yeah, that's true in most RVSM airspace. So the opposite direction traffic 1000 below will sometimes cause a quick RA return. But there are one way airways to allow more altitudes and traffic flow. Typically, the opposite direction airway (also one way) is seperated by 50 NM.

Over the Pacific, the major airlines come up with "tracks" that are used for the day. They pick the "minimum time track" for each direction. Between the west coast and Asia, the west bound flights typically fly further north to avoid the headwind while the eastbound flights fly further south to take advantage of the tailwind. So you really don't encounter any opposite direction traffic over the Pacific. This is especially true in the winter months when the wind is the strongest. Because of this, you can fly the same direction with 1000 ft seperation.