From reading this thread and others, I understand you can descend to the MSA altitude when within 25 NM of the center of the MSA. In the US, that is not permitted.
From reading this thread and others, I understand you can descend to the MSA altitude when within 25 NM of the center of the MSA. In the US, that is not permitted.
Any idea what is the reason? I guess you can still use it for emergencies without having to cancel bellow radar altitude, if there is a rule that says you always need to stay within radar & radio altitudes (MVA/MEA) to fly in controlled airspace, then descending to lower altitudes is likely not possible (MORA, MESA, MSA, MOCA…) but that would be a funky airspace design 
What is the lowest IFR altitude you can plan and/or fly in US when not on victor airways and where do you get it? do ATC publish terminal & route sectors radar MVA? can you use these for planing?
In the US, that is not permitted.
It’s not permitted in “normal European IFR” either.
At your calculated TOD you request descent.
You know what the MSA is in that 25NM circle because it is published. It is not part of the IAP so you cannot just descend to it without ATS approval. (If it is CAS). OCAS you would not need approval but you would be wise (IMO) to get the descend at your discretion, no conflicting traffic detected.
As a pilot, ATSOs are your friends, not your enemies. At least that’s how we think of them here.
On conventional nav aids, you can’t operationally descend to 25nm MSA, you are likely to lose radio communication & navigation anyway, so one is restricted to MEA or “line of sight” (VOR, VHF), of course it’s usable for emergencies like icing…when you get “cleared for approach” on conventional procedural approach, I am assuming the aircraft will be joining IAF via some STAR or Airway, so zero ambiguity how low you can descend, it’s written on the Jepps chart
Ignoring the case of UK & France (not sure if US & Germany have any of this?) where you can have a conventional IAP not connected to Airways, Arrivals without radar service, again I am assuming the PIC knows what he is doing with his altitude when talking to FIS or AFIS in Golf…my understanding 25nm terminal MSA and +/-5nm cruise MSA are usable in these cases, say going to Scillies for NDB? or Ouessant for NDB?
On GPS, when you are “cleared for approach” to an IAF you are cleared 30nm TAA of that IAF, you can ask ATC to CLARIFY this but I had the impression it’s implicit when you hear “cleared for GPS approach”, otherwise what does this means?
The “only problem” left to discuss is when you are on “vector-to-final”, this is the confusing part:
- On RV+ILS, one can afford to stay on altitude until you intercept glide slope at FAP and descend on it but what if GS flag is ON? or not visible?
- On RV+LOC, surely things will not work out of the blue for obvious reasons, so you have to fly LOC platform altitude and hit the FAF on it’s altitude at some point?
- On RV+RNP, I once got vectored to FAF on RNP once, I don’t remember what I did exactly but it worked fine…
How low you can descend on Radar Vectoring is given by MRVA charts but ATC should be able to give you an answer, they own obstacles & traffic separation, no need to bother how low you can descend, you do as you are told…if ATC wants you to maintain altitude because someone is sitting 1kft bellow, they should say so when “clearing for approach”?
https://www.ifr-magazine.com/system/terminal-arrival-areas/
https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap5_section_4.html
IMO that’s pretty straightforward and as I have always understood it.
Ibra wrote:
On conventional nav aids, you can’t operationally descend to 25nm MSA, you are likely to lose radio communication & navigation anyway,
I agree that the primary reason the MSA is charted is to provide an emergency safe altitude, but I don’t agree with loss of com/nav. Unless the terrain is unusually difficult you are very unlikely to lose com or nav at the MSA. The theoretical height required for line of sight from 25 NM out is about 400 ft!
You are right very unlikely: on 1000ft MOC all radio signals should be ok for 40nm, especially for communication (those asking for SVFR on radio tend to do just fine under TMA or CTR ) and NavAids likely reliable and well surveyed at those altitudes if terrain is not difficult, I guess the only real limitation is radar altitude (especially with all low level filtering & decluttering), now if ATC can clear you that low under normal circumstances is a different topic
Ibra wrote:
Any idea what is the reason? I guess you can still use it for emergencies without having to cancel bellow radar altitude, if there is a rule that says you always need to stay within radar & radio altitudes (MVA/MEA) to fly in controlled airspace, then descending to lower altitudes is likely not possible (MORA, MESA, MSA, MOCA…) but that would be a funky airspace designWhat is the lowest IFR altitude you can plan and/or fly in US when not on victor airways and where do you get it? do ATC publish terminal & route sectors radar MVA? can you use these for planing?
There was a major accident with a TWA flight into KIAD in 1974 where the aircraft was cleared for the approach and slammed into a hillside. After that, the FAA changed the guidance and became very strict as to when “cleared for the approach” authorizes the pilot to descend. If the aircraft is on a published route or feeder route or a segment of the approach, only then may they descend. If they are on a random route, ATC must assign an altitude to hold until the aircraft is established on a segment of the approach. If ATC fails to assign an altitude with the approach clearance, then the last assigned altitude must be maintained until the aircraft is on a segment of the approach. So descent using the MSA is not authorized and is only available in the event of an emergency. With the introduction of TAA (Terminal Arrival Area), these segments are treated as being usable as an RNAV feeder route and as long as the aircraft is inside the TAA and cleared for the approach without any specific ATC instructions to the contrary, pilots are expected to descend to the TAA sector altitude. There was another accident in Alaska where the clearance for the approach included an ambiguous instruction to maintain an altitude that was below the TAA segment and later cleared for the approach. They hit a hill at the lower altitude. So now if one is cleared for the approach, they must not be assigned an altitude below the TAA segment and if so, the aircraft must climb to the TAA altitude. ATC phraseology was also changed (at my request) to clarify when a pilot was cleared to a fix on the approach, but at an altitude that was below the fix altitude. This is allowed if the aircraft is at or above the MVA and in a radar environment, but the clearance must include an altitude to maintain until the fix and then cleared for the approach. The assigned altitude must be at or above the first segment minimum altitude on the approach that begins at the fix. So for example, at my airport the MVA in the area is 2300. CONEL is an IF fix on the RNAV 2 at KUZA. The next fix is AZAKA and is the FAF. The crossing altitude at CONEL is 3000 and the next segment to AZAKA has a 2500 foot minimum altitude. So I can be cleared as follows by ATC: N7083N is cleared direct CONEL, maintain 2500 until CONEL, cleared RNAV RWY 2 Rock Hill.
This is all very sensible stuff, and I am sure similar procedures apply in Europe.
The challenge is to find a still-working radar controller who is willing to post details. Maybe someone can PM me Maybe @atmilatos or @Guillaume know?
In fact this stuff should be in some published ATC manual.
