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Assigned lower-than-published altitude for full IAP

Asked by: 4438 views FAA Regulations, Instrument Rating

I was doing a full RNAV approach and was instructed to fly direct to the IAF and maintain an altitude lower than the published HILO-PT altitude. The controller initially thought we were doing a vectored approach, which is why I think she gave us a lower than published altitude. I know that the pilot should maintain the assigned altitude until established on a published segment, so I was confused as to what I should do. Looking back, I should have simply verified if she wanted me at the assigned altitude for the full approach. We ended up simply maintaining our lower altitude (400' below published) and then started flying the published altitudes after we were established. My instructor wasn't too sure what the legally correct thing to do was, but we figured during debrief that it was the second best thing we could have done (first being to ask ATC) since the instructed altitude was above MSA and it would have been better than getting a pilot deviation. 1) Was ATC mistaken to give us the wrong altitude? Or did she purposely get us on an altitude to maintain until established on the published approach IAW the regs? Keep in mind that she did not say "maintain [ALT] until established" or "cross [fix] at [ALT]"; she simply instructed us to maintain a certain altitude. I assume that she made a mistake since I remember a controller instructing us to climb to maintain at or above the published entry altitude when I was doing a full RNAV a couple days ago.

2 Answers

  1. Best Answer


    John D Collins on Mar 21, 2015

    I have raised this issue at ATPAC (Air Traffic Procedures Advisory Committee) that controllers routinely clear an aircraft below charted altitudes. I think this is wrong. ATPAC is a public meeting that includes all the stake holders including the airlines, FAA HQ, controllers, NBAA, AOPA, etc and these kind of system issues are raised, discussed, and in most cases resolved, but it does take time.

    There are differences between being on vectors and flying a charted route. In the case of an airway, you may not be assigned an altitude below the MEA or as appropriate the MOCA. That exact same route could be cleared at an altitude below the MEA if the aircraft was on vectors and not assigned to fly the airway, assuming that the altitude was at or above the Minimum Vectoring Altitude, which for now is only known to the controller.

    If you are cleared to a point on the approach, ATC may assign the altitude to maintain until that point. Once beyond that point, the altitudes on the approach chart are minimums. It does not make sense to assign an altitude below a charted segment that would require a subsequent climb on a segment. So if the crossing altitude at aaaa is 4000, but the next segment to bbbbb is at 3000, it would be OK clear an aircraft direct to aaaaa at 3000, but not at 2800, which would require a climb back to 3000 after passing aaaaa. The portion of the route to aaaaa must be at or above the minimum vectoring altitude.

    I am waiting on improved guidance in this area to be published.

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  2. Alex Weeks on Mar 25, 2015

    I’ll second what John Collins said. This is common and unsafe. I’ve unofficially talked to approach designers and gotten some reasonable answers about why it can be okay. But in the end, it’s too easy for a controller to make a mistake and fly an airplane into the side of a mountain while the pilots blindly follow instructions.

    I don’t think in your case the controller necessarily made a mistake. It’s very common for a controller to issue altitudes below those published on approaches. Happens all the time. I can name airports where it happens on pretty much every approach.

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