Low altitude alert

M

ManleyD

Well-Known Member
I was flying a LOC approach a few nights ago and the weather was about 100 ft above mins. While "diving and driving" to the MDA at about 200 ft to mins, tower says " low altitude alert, minims for this approach are xyz." I wanted to get to the MDA and have a little time to look for the runway before the MAP, so I was descending quickly. We landed safetly. After reviewing the approach with the captain to make sure we didn't do anything wrong, we determined that............ We didn't do anything wrong. I didn't descend below the MDA and I commenced the descent to the MDA at the appropriate point as depicted on the plate.

I've heard ATC issue this warning before but not toward me. I'm curious what triggers this alert when the approach is being flown correctly. Rapid rate of descent? Is it a precautionary warning?
 
Rapid rate . The computer projects that if you keep up the profile that you'll meet terra firma before the runway. Its a required call
 
That explains it. It kind of felt like I was being scolded for doing something wrong, especially with the "minimums for this approach are xyz" part. Which is why I asked. But it makes sense. Thanks!
 
On a tower tour at my airport the controller explained to me that when we are issued low altitude alert it is because a altitude alert system has told them we are too low and they are required to tell us. The system has a series of boxes down the approach path saying what is too low so if your angle of descent is greater than what the system expects you will clip the edge of a box which sets off their alarm.
 
genot said:
Rapid rate . The computer projects that if you keep up the profile that you'll meet terra firma before the runway. Its a required call
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Yup. I get that all the time on steep and short step downs at certain airports.
 
Obviously in this case it was safe, but I'm surprised like Tcas there isn't a mandatory go-around procedure upon receiving that warning.

Seeing as there is mandatory everything else these days
 
canadian_atc said:
Obviously in this case it was safe, but I'm surprised like Tcas there isn't a mandatory go-around procedure upon receiving that warning.
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Onboard equipment (EGPWS/TAWS) is probably a much better judge than a ground-based system—and below 500' AGL in IMC, a go-around for any EGPWS warning where I work is mandatory.

If we're (transport category, anyway) really in trouble, the odds are that you're going to tell us while our onboard boxes are also a'squawkin' about terrain, terrain, pull up.
 
In the US, controller judgment can be used to determine whether the situation is actually unsafe or if perhaps the alarm is just a nuisance (someone diving to the MDA/next altitude on a non precision approach for example). The alarms go off on visual approaches too.

2−1−6. SAFETY ALERT
Issue a safety alert to an aircraft if you are aware the
aircraft is in a position/altitude which, in your
judgment, places it in unsafe proximity to terrain,
obstructions, or other aircraft. Once the pilot informs
you action is being taken to resolve the situation, you
may discontinue the issuance of further alerts. Do not
assume that because someone else has responsibility
for the aircraft that the unsafe situation has been
observed and the safety alert issued; inform the
appropriate controller.
Click to expand...

The last part of that paragraph is really fun, because we're required to inform the responsible controller when we observe an alarm from our position (the alarms sometimes go off at multiple positions, for example the Tower's radar display and the approach controller's). This leads to a situation where, when there's an actual safety alert needed to be issued, the controller issuing the alert is probably getting at least one override call in their headset while trying to talk to the affected airplane.
 
9 years ago over in Iraq, we had a jet nearly hit the ground during a night instrument approach. As the pilot was being directed to final for a non-precision (ATC radar out, reporting points in use); he'd had a long night mission and was pretty fatigued. After reporting established on the arc, he was given approach clearance, report FAF inbound. He commenced a descent from there and turned from the arc onto final (dark night, IMC). Unbeknownst to him his crosscheck had broken down, and as he was concentrating on the TACAN (VOR) intermittently breaking lock as he was trying to roll out on the inbound course, he missed the fact that he just blew through the intermediate altitude, and was headed at 1500 fpm to the ground below. The PAR radar was down, and some workers were doing maintenance on it. As you all know the PAR radar, unlike a terminal radar, has a very limited field of view up the glidepath (much like an ILS localizer)....it can't see traffic outside that, nor does it want to....it's job is to direct one aircraft at a time down the final approach path to a precision landing.

Anyhow, the workers get the part installed that they need, and fire up the PAR scope. A 19 yr old Airman ATC apprentice, is up on approach frequency to coordinate with approach about their out-of-service surveillance radar. The PAR scope comes on, but it's only getting tested, so he's not paying too much attention to it, but he notices a secondary blip (the IFF of the A-10 on approach), just as it comes into the edge of his scope. The PAR radar had been down, since it had been giving erroneous target data from radar returns. The Airman sees the blip reading 5100' and descending. Not knowing if this is correct so far as the radar goes (whether it's working or not), but knowing full well that the altitude (if correct) is well below MVA, puts out a call on Guard "On Guard, aircraft approaching final at Kirkuk, altitude alert, check altitude, terrain alert. Climb to 6400 immediately." The pilot in the A-10 hears this and, cross-checking his altitude, sees that it's him that's being talked to. He commences a pull while simultaneously rolling wings-level, and bottoms out at 150 AGL in IMC , it's later determined.
 
Autothrust Blue said:
Onboard equipment (EGPWS/TAWS) is probably a much better judge than a ground-based system—and below 500' AGL in IMC, a go-around for any EGPWS warning where I work is mandatory.

If we're (transport category, anyway) really in trouble, the odds are that you're going to tell us while our onboard boxes are also a'squawkin' about terrain, terrain, pull up.
Click to expand...

I would never be able to land at our destinations if that was the case.
 
MikeD said:
9 years ago over in Iraq, we had a jet nearly hit the ground during a night instrument approach. As the pilot was being directed to final for a non-precision (ATC radar out, reporting points in use); he'd had a long night mission and was pretty fatigued. After reporting established on the arc, he was given approach clearance, report FAF inbound. He commenced a descent from there and turned from the arc onto final (dark night, IMC). Unbeknownst to him his crosscheck had broken down, and as he was concentrating on the TACAN (VOR) intermittently breaking lock as he was trying to roll out on the inbound course, he missed the fact that he just blew through the intermediate altitude, and was headed at 1500 fpm to the ground below. The PAR radar was down, and some workers were doing maintenance on it. As you all know the PAR radar, unlike a terminal radar, has a very limited field of view up the glidepath (much like an ILS localizer)....it can't see traffic outside that, nor does it want to....it's job is to direct one aircraft at a time down the final approach path to a precision landing.

Anyhow, the workers get the part installed that they need, and fire up the PAR scope. A 19 yr old Airman ATC apprentice, is up on approach frequency to coordinate with approach about their out-of-service surveillance radar. The PAR scope comes on, but it's only getting tested, so he's not paying too much attention to it, but he notices a secondary blip (the IFF of the A-10 on approach), just as it comes into the edge of his scope. The PAR radar had been down, since it had been giving erroneous target data from radar returns. The Airman sees the blip reading 5100' and descending. Not knowing if this is correct so far as the radar goes (whether it's working or not), but knowing full well that the altitude (if correct) is well below MVA, puts out a call on Guard "On Guard, aircraft approaching final at Kirkuk, altitude alert, check altitude, terrain alert. Climb to 6400 immediately." The pilot in the A-10 hears this and, cross-checking his altitude, sees that it's him that's being talked to. He commences a pull while simultaneously rolling wings-level, and bottoms out at 150 AGL in IMC , it's later determined.
Click to expand...


I sincerely hope he got a medal, or at least a case of beer.


Sent from 1865 by telegraph....
 
scooter2525 said:
That's a fun airport to fly into. At night, not so much. Very dark.
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Yeah we had to do the circling this morning out over the mudflats with the GPWS all getting up in our business again. I'm not sure how the 1.5 mile radius doesn't clip the hills to the south.
 
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