Altitude/Terrain Alert?

[cfii2007]

I was shooting an approach with my student today and the tower gave us a terrain alert. We were on a VOR approach and leveled off prior to the MDA.

I was wondering why we were issued this, since we at no time descended below the MDA? I'm assuming the TERPS regulate the amount of obstacle clearance for each type of approach and segment, unless I am missing something?

[PanJet]

I'm not ATC, but this has happened to me before as well. Apparently there was an issue with ATC's equipment, and they knew it, but were still obligated to notify you with a verbal announcement.

The scary part was it happened when we were shooting an ILS in actual. Let me tell you there's nothing scarier than hearing "Terrain alert! Check altitude immediately!" when you're in the clouds. We were dead on localizer and glide slope, however, and had to trust it until we broke out.

[tgrayson]

Originally Posted by cfii2007

was wondering why we were issued this, since we at no time descended below the MDA? I'm assuming the TERPS regulate the amount of obstacle clearance for each type of approach and segment, unless I am missing something?

Was there an ILS to the same runway? Radar facilities have an Minimum Safe Altitude Warning system which often sounds when you have a descent rate that looks scary, such as what you get on an non-precision approach. The warning isn't that you descended below a safe altitude, but it looks like you might if you keep doing what you're doing.

When shooting the LOC portion of an ILS, good policy is to make sure ATC knows that you're doing this, for the same reason.

[cfii2007]

We were shooting a VOR approach in IMC, and yes, it kinda freaked me out a bit.

There is an ILS at the field for the opposite runway.

[taseal]

a 496 (or 396 I think too?) could be really useful here I guess

[tgrayson]

Originally Posted by cfii2007

We were shooting a VOR approach in IMC, and yes, it kinda freaked me out a bit.

There is an ILS at the field for the opposite runway.

From the Instrument Flying Handbook:

A valuable service provided by the automated radar equipment at terminal radar facilities is the Minimum Safe Altitude Warnings (MSAW). This equipment predicts your aircraft’s position in 2 minutes based on present path of flight — the controller will issue a safety alert if the projected path will encounter terrain or an obstruction. An unusually rapid descent rate on a nonprecision approach can trigger such an alert.

[cfii2007]

Thanks!!!

[SIUav8er]

Originally Posted by tgrayson

From the Instrument Flying Handbook:

A valuable service provided by the automated radar equipment at terminal radar facilities is the Minimum Safe Altitude Warnings (MSAW). This equipment predicts your aircraft’s position in 2 minutes based on present path of flight — the controller will issue a safety alert if the projected path will encounter terrain or an obstruction. An unusually rapid descent rate on a nonprecision approach can trigger such an alert.

Thats great! I get low altitude alerts quite a bit when doing non precision approaches (of course im always at the published MDA when this happens). It kinda freaks the students out cause I had no way of explaining what was going on!

Id just tell 'em "ATC dont know sheet!" lol. [sarcasm]