That was TWA514, it was 1974. That incident led to FAR 91.175 (h) (2) (i).Required to give you an altitude to maintain until you're established on the approach. Brought about because of an airline descended early on approach into Dulles I think it was and flew into terrain. During the 50s or 60s it occurred. As a result you receive an altitude to maintain.
Also you must maintain the altitude assigned until you have course guidance for the final approach course. The reason is most often a TERPS/MVA issue. For example, the MVA around the airport is 5000, but the GS intercept for its ILS is 4700. If you went to 4700 before being near the final approach course, ATC would get an MSAW (minimum safe altitude warning) alert.
Why do controllers say "cross (initial) at or above (altitude), cleared (rnav xyz) approach" when that altitude is already on the plate?
This is a great example. In that situation, you can't descend until you are established on a published segment of the approach, so you would have to descend from 6000 to 2700 within 5 nm between IYBEP and EQAXO. That's 660 feet per nautical mile or 1320 feet per minute if your ground speed is 120 knots during the descent. Pretty steep, especially compared with the average 200 feet per nautical mile you have to get down the rest of the way to the airport elevation by the end of the approach procedure.You're arriving from the southeast and are direct to IYBEP. Maybe you're 20 nm from IYBEP at 6000. If the controller just clears you for the approach without including an altitude, do you descend? When? To what altitude?
Why do controllers say "cross (initial) at or above (altitude), cleared (rnav xyz) approach" when that altitude is already on the plate?
Required to give you an altitude to maintain until you're established on the approach. Brought about because of an airline descended early on approach into Dulles I think it was and flew into terrain. During the 50s or 60s it occurred. As a result you receive an altitude to maintain.
That was TWA514, it was 1974. That incident led to FAR 91.175 (h) (2) (i).
Explained in post 3, sigh, and other posts, but it's POA, time to beat the horsey.
Some folks may prefer to read an entire discussion before responding. Some folks prefer to read and respond in sequence.
Yup. I think it's important though to cover it from both ends. Requiring ATC to comply with the intent of 91.175 (h) (2) (i) by requiring them to issue an altitude to maintain until established is a pretty good idea. And requiring pilots to maintain last altitude until established if ATC f**ks up and forgets is a pretty good idea.Which should make the altitude restriction "cross (initial) at or above (altitude), cleared (rnav xyz) approach" issued with the approach clearance unnecessary.
I think it's 91.175(i) as in the lowercase letter after (h) rather than (i) as in the first lowercase Roman numeral as a subdivision of (h)(2). It's badly formatted in every source I can find online, but the sequence of (j) being next shows where the (i) belongs. The good news is that we are supposed to trust the same people who created that problem to reorganize and simplify the tax code.Yup. I think it's important though to cover it from both ends. Requiring ATC to comply with the intent of 91.175 (h) (2) (i) by requiring them to issue an altitude to maintain until established is a pretty good idea. And requiring pilots to maintain last altitude until established if ATC f**ks up and forgets is a pretty good idea.
But then to further reduce the chance of such a fatal assumption being made by a pilot, the crossing restriction is apparently required by ATC order when you're not on a published route. (See post #11 by @roncachamp.) What does the ATC order actually say? Does it allow for "descend and maintain X" to get us close enough to the first altitude on the IAP or does it always require "cross FIX at or above X"?
Thats it. Something I might add is it is very common for a controller to include "an altitude to maintain...." when it's not necessary to because the aircraft is established. This altitude until established is serious stuff and controllers get it hammered in early in training. Don't confuse a controller giving it when it seems not necessary as some change in some rule or some random interpretation. ALWAYS giving it guards against making boo-boo'sThe ATC order says:
For aircraft operating on unpublished routes, issue the approach clearance only after the aircraft is:
1. Established on a segment of a published route or instrument approach procedure, or
2. Assigned an altitude to maintain until the aircraft is established on a segment of a published route or instrument approach procedure.
No mention of altitude is needed in the first condition. In the second condition, if X is the appropriate altitude, and the aircraft is still above X, then "cross PHYXE at or above X, cleared RNAV runway 36 approach" is good phraseology. If the aircraft is already level at X, then "maintain X until PHYXE, cleared RNAV runway 36 approach".
Thats it. Something I might add is it is very common for a controller to include "an altitude to maintain...." when it's not necessary to because the aircraft is established. This altitude until established is serious stuff and controllers get it hammered in early in training. Don't confuse a controller giving it when it seems not necessary as some change in some rule or some random interpretation. ALWAYS giving it guards against making boo-boo's
Don't think I've ever heard that, it certainly would sound funny. I shouldn't have used the "established" example. My bad. I was getting back to the OP's original question "Why do controllers say "cross (initial) at or above (altitude), cleared (rnav xyz) approach" when that altitude is already on the plate?" That would sound like say "cross [fix] at or at or above" and then duplicate the altitude on the chart. Maintain [same altitude as the chart] until [fix]. This when already established so not necessary.Outside of a crossing restriction, how would you issue an altitude to maintain until established on a segment of a published route or IAP to an aircraft that is established on a segment of a published route or IAP?
Why do controllers say "cross (initial) at or above (altitude), cleared (rnav xyz) approach" when that altitude is already on the plate?
I dont know the history but, based on the way most instructions of this type come about, a couple of guesses: accidents and incidents when people started descending early for varying reasons from misreading the plate to confusion - it’s a reminder; with vectoring and traffic, the altitude given may be higher or lower that the one on the plate; there’s a value to always doing it the same way each time, giving the basic numbers - less likely to make a mistake.Don't think I've ever heard that, it certainly would sound funny. I shouldn't have used the "established" example. My bad. I was getting back to the OP's original question "Why do controllers say "cross (initial) at or above (altitude), cleared (rnav xyz) approach" when that altitude is already on the plate?" That would sound like say "cross [fix] at or at or above" and then duplicate the altitude on the chart. Maintain [same altitude as the chart] until [fix]. This when already established so not necessary.
Yeah. When being vectored to or direct to, both of which have you not on published segements, giving the altitude is absolutely mandatory, even if it is the same altitude that is published for that segement. For an aircraft that is already established on a published segement it would be redundant unless the controller needed the aircraft at a different altitude for traffic. Routinely Including the altitude with all clearances, even when unnecessary, would guard against the controller forgetting to when necessary and the pilot misreading the chart.I dont know the history but, based on the way most instructions of this type come about, a couple of guesses: accidents and incidents when people started descending early for varying reasons from misreading the plate to confusion - it’s a reminder; with vectoring and traffic, the altitude given may be higher or lower that the one on the plate; there’s a value to always doing it the same way each time, giving the basic numbers - less likely to make a mistake.
As already mentioned:Why do controllers say "cross (initial) at or above (altitude), cleared (rnav xyz) approach" when that altitude is already on the plate?
Yeah. There aren't a lot of mandatory altitudes out there, but relieving the pilot of complying with the 'below' part of one when it's not necessary because of traffic is a nice thing to do.As already mentioned:
-It's in the book as a requirement
-Is needed when not on a published segment of the approach
-clears up any possible confusion
Didn't see mentioned:
-I issue at or above so the pilot doesn't have to worry about being precisely at the altitude by reaching the fix. One less thing to concentrate on especially when you have not far distance wise to lose quite a bit of altitude. A minor pet peeve of mine is when a controller tells an aircraft already at the altitude "at or above". Like the pilot is just going to arbitrarily climb up to start the approach.