Altitude alert

MooneyDriver78

MooneyDriver78

En-Route
Joined
Aug 13, 2013
Messages
4,538
Display Name
Display name:
Tom
Was on a real LPV approach, at 800-900' the tower calls and says altitude alert, I acknowledge with roger but was dead on the glide slope. No warnings from my garmin avionics, when I tell them I'm on track, they seem to say they always give warnings, I was too busy to follow up...is this normal practice?
 
Yes ,at some airports ,even if on the glide slope tower will give you a warning,must have to do with their radar.
 
Software predicts where your plane will be in a certain number of seconds and alerts the controller if your flight path will intercept terrain. I'm not sure if the controller can suppress this. Consider it as a belt-and-suspenders feature for your safety. Look up Low Altitude Alert in the Pilot/Controller lossary.

Bob Gardner
 
Depending on location and RADAR the computer may update every second or every 7 seconds. Our computer averages it and dispenses the alert. It isn't suppressible and it is an alert we are liable for is not issued should something go wrong. The math includes the MVA which isn't charted/TERPED on the approach.

Long story short, its easy to descend somewhat rapidly for several seconds, level, be on glide slope and trigger the computer and it'll still process the alert.

Happens far less at TRACONS with fusion with one second mode C updates.
 
In other words if the computer senses you are getting low to the ground too fast and triggers the alarm, a flashing red "LA" will appear by your data tag along with an aural alarm; when that happens, controllers are bound to transmit a low altitude alert warning to you.

Happens all the time here.


By the way...if you ever saw the movie Pushing Tin, you've seen what happens although that was a "CA" (collision alert) instead of an "LA". And unlike the movie, when that happens all the other controllers don't gather round to watch. CA alarms go off all the time if the computer senses two planes are getting close to one another and even though the controller has given traffic to both aircraft and they have each other in sight.
 
I am not thrilled with the low altitude alert system. The way it is now, there does not seem to be adequate means to decide if it is a bonafide warning and you are truly too low, or it is just a spurious alert.
I had one on the approach going into Brown field years ago, and heard another pilot get it there too. I was level, having already made the minimum for the segment approaching the VOR so I don't think it was the system was predicting a ground collision with a VSI of 0. (it was imc so I had no visual cues)
I reported the Kohlsman setting and altitude, tower had no objection so I continued. Beyond that what else can be done? The radar altimeter does not work that high.
I always wondered what if the system was right and I was about to take out a tower or hill because my air data was off.
Should we go missed on these and somehow verify our position and altitude beyond what is already available to us? Or does the LAE system need tweaking?
It's pretty unnerving to get this while in the soup.
 
Let'sgoflying! said:
I am not thrilled with the low altitude alert system. The way it is now, there does not seem to be adequate means to decide if it is a bonafide warning and you are truly too low, or it is just a spurious alert.
I had one on the approach going into Brown field years ago, and heard another pilot get it there too. I was level, having already made the minimum for the segment approaching the VOR so I don't think it was the system was predicting a ground collision with a VSI of 0. (it was imc so I had no visual cues)
I reported the Kohlsman setting and altitude, tower had no objection so I continued. Beyond that what else can be done? The radar altimeter does not work that high.
I always wondered what if the system was right and I was about to take out a tower or hill because my air data was off.
Should we go missed on these and somehow verify our position and altitude beyond what is already available to us? Or does the LAE system need tweaking?
It's pretty unnerving to get this while in the soup.
Click to expand...

Which is why the modern IFR pilot should have terrain/obstacle avoidance on board. I have it on three devices (none depend on air data), the official panel plus unofficial tablets; won't leave home without them.
 
Last edited:
If I wasn't confident of my altitude and dead on the glide slope I would have aborted the approach.
 
Happens a lot, especially on circling approaches.

My understanding was that if the gizmos throw out an alert they have to tell you, even if they know what you're doing and totally expect you to be in the pattern at 550 ft AGL.
 
A simple way to check your altitude on final is you should be at 300' agl one mile out, 600' agl two miles out, 900' three miles out frpm runway threshold, etc. as a simple back-up (situational awareness) check of your altitude. 5 miles out you'd be 1500' agl.
 
Last edited:
BWI controller might have saved my butt with a low altitude alert call - my glideslope had failed, without indication. I was an "advanced" instrument student, and my CFII was relaxed, since I had it "nailed" - we were night, and in actual. Reverted to the localizer, as I recall.
 
Sundancer said:
BWI controller might have saved my butt with a low altitude alert call - my glideslope had failed, without indication. I was an "advanced" instrument student, and my CFII was relaxed, since I had it "nailed" - we were night, and in actual. Reverted to the localizer, as I recall.
Click to expand...

It's REAL important to cross check altitudes on glideslope.

I had a false indication at San Jose once show I was far above the glideslope -- and that's what the instructor focused on. I didn't feel it was right -- it seemed too low, too fast -- and when we passed the FAF it became obvious the altitude was wrong. We were in fact below glide. At that point, I reverted to the LOC approach.

Fortunately, this was in VMC, so we were never in any risk of terrain, and we were still fairly far out, more than 2000 feet above terrain. The LOC minimum at that point was 1000 (though we had clearly busted the 2700 foot minimum prior to the FAF).

I should have recognized the problem earlier. Since the FAF crossing was 2700, there is no way I should descend below 2700 before getting there.

This was on the "second" glideslope (NAV2; this airplane had two of them), so it wasn't the GPS CDI being set wrong. Even if it was, that kind of excursion is far above what might be expected. And the LOC was fine, so it wasn't a mistuned receiver.
 
Sundancer said:
BWI controller might have saved my butt with a low altitude alert call - my glideslope had failed, without indication. I was an "advanced" instrument student, and my CFII was relaxed, since I had it "nailed" - we were night, and in actual. Reverted to the localizer, as I recall.
Click to expand...
Yep. That happened to me too. Not as an instrument student. Actual approach in the clouds. Glideslope needle came alive normally, centered as I crossed the OM at intercept altitude ... and stuck there.
 
I bet billions of dollars spent on ADS-B will fix it. ADS-B fixes everything, even the common cold! ;)
 
The system seems to have some issues with approaches. If you are below the radar vectoring altitude in a sector (something not printed on pilot charts) it freaks out and sounds alarms even if you are at or above the altitude charted for a segment of an approach plate.

A few times now I've gotten "low altitude alert, commence climb immediately" from ATC. After pointing out that I'm at the correct altitude for the approach they say "Oh yeah, OK, your good, well regs say if the alarms go off we have to tell you and tell you to climb."

Better safe than sorry for sure, but this has started happening enough to be a distraction during approaches.
 
midlifeflyer said:
Yep. That happened to me too. Not as an instrument student. Actual approach in the clouds. Glideslope needle came alive normally, centered as I crossed the OM at intercept altitude ... and stuck there.
Click to expand...

Me too, once. Same stuck GS needle smack in the middle, no flag, in low IMC.
Got suspicious when it seemed too good to be true, so verified it was not responding to power changes and reverted to the LOC.
Nowadays I have terrain and obstacle colors and alerts, on three separate devices, so I feel a bit safer. But you never know, so always respect and suspect, as they say in Russian. :)
 
we get that every now and then from controllers too, often times they say its most likely due to the descent rate. As some others its predictive software, so even if we are planning on leveling out at 3,000 feet but because of our rate of descent it predicts some sort of impact within a certain time frame they'll give us the alert, even though in all reality if we level off at the the correct altitude we would never intercept.
 
JustinD said:
its most likely due to the descent rate. As some others its predictive software, so even if we are planning on leveling out at 3,000 feet but because of our rate of descent it predicts some sort of impact within a certain time frame they'll give us the alert,
Click to expand...
This is when I have seen it. If you dive and drive and your dive is too steep, it seems to trigger an alert.
 
You must log in or register to reply here.
Back
Top