Descend to MSA when "cleared approach"

[president]

@ aterpster,

platform altitude is just a slang for initial approach altitude. heard that it originates from the uk. ICAO do refer to the term on top page 9 in this doc. But itīs nothing official.

http://www.icao.int/safety/RunwaySaf...iderations.pdf

[FlightDetent]

Just that the US meaning of the term differs from what you are probably used to. Not to derail the thread any further, but in FAA parlance, MSA is not a procedural altitude. It is merely an altitude which should keep you out of the weeds if you are off the procedural track and within 25 nm of the NAVAID depicted.

From FAR 97.3 Quote:
MSA means minimum safe altitude, expressed in feet above mean sea level, depicted on an approach chart that provides at least 1,000 feet of obstacle clearance for emergency use within a certain distance from the specified navigation facility or fix.

Interesting. I noted the reference to AIM in the previous post too, different ways to skin a cat.

For where I come from (both training and operations) MSA is calculated in the same manner, providing 1000 ft obstacle clearance. Given the fact, that intermediate approach segment MOC is 500 ft - just for comparison, I am happy to use MSA as an operational altitude when the situation of the day requires to do so.

This would be illegal in the US, ok. Learn something every day: ticked.

[aterpster]

president:

Thanks for the reference. I quote the pertinent language:

An aircraft can either self position for an approach or be vectored. Before leaving the Initial Approach Altitude (also known as Platform Altitude) the aircraft must be lined up with the runway and at an appropriate distance. If the aircraft is not in the correct position the final descent can not be commenced as the aircraft may be outside of the protected area, hence terrain separation can not be assured. A descent at this point would be dangerous, particularly if in Instrument Meteorological Conditions.

I am not sure what the author is trying to say. In any case, it would nave no application in FAA controlled airspace. We learned the lesson the hard way with the TWA 514 CFIT. Those AIM cites above, are almost verbatim quotes of federal aviation regulations written after TWA 514.

[aterpster]

FlightDetent:

For where I come from (both training and operations) MSA is calculated in the same manner, providing 1000 ft obstacle clearance. Given the fact, that intermediate approach segment MOC is 500 ft - just for comparison, I am happy to use MSA as an operational altitude when the situation of the day requires to do so.

This would be illegal in the US, ok. Learn something every day: ticked.

A further bit of clarification. In TERPs, and I presume in PANS-OPS as well, required obstacle clearance (ROC) in feeder routes and airways must have at least 2,000 feet of ROC in Designated Mountainous Areas (DMAs) and 1,000 feet elsewhere. MSAs always have 1,000 feet, even in DMAs, which makes them especially non-operational in DMAs.

The FAA is going increasingly to Terminal Arrival Areas (TAAs), which are operational altitudes that replace MSAs and have 2,000 feet of ROC in DMAs. TAAs don't fit everywhere because they have to meet descent gradient requirements (MSAs don't) and the affected ATC facility has to sign off on TAA procedures. Attached is am example of a TAA procedure. (Some other countries are also using the TAA concept instead of MSAs, at least with some procedures.)

[Zaphod Beblebrox]

My take on this is No you many not descend to the MSA. I base this answer on the following:
(US rules only)

14 CFR 91.175 - Takeoff and landing under IFR

(i) Operations on unpublished routes and use of radar in instrument approach procedures. When radar is approved at certain locations for ATC purposes, it may be used not only for surveillance and precision radar approaches, as applicable, but also may be used in conjunction with instrument approach procedures predicated on other types of radio navigational aids. Radar vectors may be authorized to provide course guidance through the segments of an approach to the final course or fix. When operating on an unpublished route or while being radar vectored, the pilot, when an approach clearance is received, shall, in addition to complying with § 91.177, maintain the last altitude assigned to that pilot until the aircraft is established on a segment of a published route or instrument approach procedure unless a different altitude is assigned by ATC. After the aircraft is so established, published altitudes apply to descent within each succeeding route or approach segment unless a different altitude is assigned by ATC. Upon reaching the final approach course or fix, the pilot may either complete the instrument approach in accordance with a procedure approved for the facility or continue a surveillance or precision radar approach to a landing.

Different countries may have different rules but in the US there was a famous accident at Washington Dulles. A TWA 727 crashed short of runway 13. It was a CFIT accident where the aircraft descended to the initial approach altitude while on vectors. There was ridge line between the aircraft's position and the runway and they hit just below the crest. This was after cockpit voice recorders but before ground proximity warning systems.

[JammedStab]

The answer is....it depends on the country.

[A Squared]

Originally Posted by galaxy flyer

In the US, TW514 smashed into a ridge doing just this.

Actually, no they didn't, they descended well below the MSA. If they had remained at the MSA, they wouldn't have hit anything. From the chart ATERPSTER posted, I believe the relevant sector MSA was 3300 MSL. If not it was 2600 MSL Either altitude would have kept them clear of terrain. The hill they hit was slightly less than 1800 ft MSL

[galaxy flyer]

The OP's proposition was to descent to "platform" altitude upon receipt of the approach clearance--which exactly what TW 514 did, such as a platform existed. And when would suggest they left 3300 feet? Besides, TERPS does not authorize the MSA as an operational altitude and it was trained that way, in any case.

GF

[AerocatS2A]

No, the OP mentions the platform altitude but their actual proposition is to descend to the MSA, which may or may not be ok depending on where you are flying. Where I fly, it is not ok, we are expected to maintain the last assigned altitude until on the approach. Descending below the MSA in IMC would be stupid regardless of where you are flying.

[winterOPS]

I am also curious of this question. How ever I cant find a legal reference amongst the answers. I think the question is within "EASA land" tough... and therein it might by divided as EASA regulation and/or national regulations.

During training I learnt that once cleared for approach you can follow the altitude restrictions stated on the plate how ever if I recall it correctly every time this happened it was coupled to an arrival route. So this option everybody more or less agree on

How ever the question, under radar vectors could you apply this or not? And if yes where does it legally say so...

if looking though Eurocontrols "ICAO Phraseology Reference Guide / ALL Clear" it does imply that you may not descend below cleared altitude even tough you are cleared for approach.

So, if vectored "too high" for intercept from below ask for descend...

Have a look at page 17

http://www.skybrary.aero/bookshelf/books/115.pdf


Might this be a question to rise on the ATC forum as well?

[oggers]

"You know, according to this dumb sheet it says thirty four hundred to Round Hill --- is our minimum altitude..[but]..when he clears you, that means you can go to your initial approach altitude." Said the captain of TWA514 as he passed 3000' descending 1800', 30 miles out in the mountains of Virginia on 'approach' to Dulles.

Well as GF, aterpster and intruder have explained the FAA have nailed this one. You cannot leave assigend alt until established.

Despite suggestions it may be kosha in other countries, nobody has come up with a single reference to back that opinion. So the answer is still no.

On the other hand a 'cruise clearance' (USA again) clears the pilot for the approach and descent to MEA at pilots discretion. But you don't get one of those whilst being vectored.

[Checkboard]

In the UK, the Manual of Air Traffic Services (CAP 493), says:

The controller shall use one of the following techniques when issuing a clearance to the pilot to descend on the ILS/MLS glidepath:

•  
  • (1) Clear the pilot for the ILS/MLS approach only if a descent instruction has been issued to the level published in the ILS/MLS instrument approach procedure at the final approach fix, or to a lower level permitted by the aerodrome’s SMAC; or
  • (2) Issue a conditional clearance to the pilot to descend on the ILS/MLS glidepath once established on the localiser; or
  • (3) When it is necessary to ensure that an aircraft joining the ILS/MLS does not commence descent until specifically cleared, solely instruct the pilot to report established on the localiser and to maintain the previously assigned level. Subsequently, the pilot shall either be cleared to descend on the glidepath or given appropriate alternative level instructions.

So you should (in the UK) never be given "Cleared Approach", unless you have also been cleared to descend to the platform altitude (precisely due to this confusion). You should (in your example), if you are cleared to descend to 4000' and intercepting an approach with a 3000' platform, be cleared "once established, descend with the glide". In other words - the 4000' is limiting until conducting the approach - i.e. on the glidepath.

This is because the approaches are surveyed with regard to terrain clearance, but not necessarily airspace. You may thus have a 2500' platform shown on the plate, but the lower limit of controlled airspace is 3000' and VFR traffic may be transiting under arriving traffic at 2500' outside controlled airspace.

[RAT 5]

Are you ever cleared for 'Approach', unless visual? Are you not cleared for an ILS, or VOR, or RNAV, or NDB approach. Is there not always a suffix? Often there is a request to call established on the final track, and then given descent clearance from your last cleared ALT. IT maybe you'll be cleared to establish and then descend, but always on the XYZ type of approach aid.

[A Squared]

Originally Posted by galaxy flyer

The OP's proposition was to descent to "platform" altitude upon receipt of the approach clearance--which exactly what TW 514 did, such as a platform existed.

Again, no, it is not. "platform" altitude is an unofficial term which apparently may mean different things to different people, and it has absolutely no meaning in the context of US TERPS. It is significant that aterpster, one of the more knowledgeable people in the US about TERPS issues had never heard of "Platform Altitude".

There are some pretty broad clues what the OP meant when he said "platform altitude". I'll quote them for you. The first is the thread title:

'Descend to MSA when "cleared approach"'

Then in the original post, tha actual question being asked:

" Can you legally descend to the MSA before you are established? "

Did you notice that "MSA" keeps popping up?

That’s what the question is about; descending to MSA and that's not what caused TWA 561 to crash. They descended below MSA to the intermediate approach altitude. You'll notice that nowhere does the OP suggest or asking about descending to an intermediate altitude prior to being established on that intermediate approach segment.

Originally Posted by galaxy flyer

And when would suggest they left 3300 feet? Besides, TERPS does not authorize the MSA as an operational altitude and it was trained that way, in any case.
GF

I never claimed it was legal to descend to MSA in the US. As others have pointed out it's not a procedural altitude in the US I'm only saying that if they had descended to the relevant MSA and maintained that altitude until established on the approach, (which is what is being proposed by the OP) they would not have crashed. That's not a trivial distinction.

[A Squared]

Originally Posted by oggers

Despite suggestions it may be kosha in other countries, nobody has come up with a single reference to back that opinion. So the answer is still no.

Here's one. Transport Canada AIM RAC 9.3.

A clearance for an approach may not include any intermediate altitude restrictions. The pilot may receive this clearance while the aircraft is still a considerable distance from the airport, in either a radar or non-radar environment. In these cases, the pilot may descend, at his/her convenience, to whichever is the lowest of the following IFR altitudes applicable to the position of the aircraft:

(a) minimum en route altitude (MEA);

(b) published transition or feeder route altitude;

(c) minimum sector altitude (MSA) specified on the appropriate instrument approach chart;

(d) safe altitude 100 NM specified on the appropriate instrument approach chart;
or

(e) when in airspace for which the Minister has not specified a higher minimum, an altitude of at least 1 000 ft above the highest obstacle within a horizontal radius of 5 NM (1 500 ft or 2 000 ft within designated mountainous regions, depending on the zone) from the established position of the aircraft.

Doesn't get much clearer than that.

[RAT 5]

I interpret this Canadian text to mean: you are cleared for an approach of whatever type. You can descend at pilots' discretion so as to safely establish on the approach at a safe altitude. You are responsible for determining what that is. The criteria are written down.

No where in that text are you operating at an ATC cleared altitude (below your cruise level) on a commanded heading to establish on the final track. It's not quite apples & apples.
However, your example might be concentrating on the 'MSA' element of the text. If so I defer to you.

[aterpster]

A Squared:

I never claimed it was legal to descend to MSA in the US. As others have pointed out it's not a procedural altitude in the US I'm only saying that if they had descended to the relevant MSA and maintained that altitude until established on the approach, (which is what is being proposed by the OP) they would not have crashed. That's not a trivial distinction.

Having been trained many times by the same training department that trained the TWA 514 crew, I doubt they had any training on MSAs, or even how to pick them off the Jepp chart (which portrayal of MSAs was quite bad in those days.) They focused on three critical altitudes in the plan view leading to ROUND HILL. Had they selected any one of those three altitudes as their minimum altitude until ROUND HILL, they would have been home free. Some on the accident investigation team speculated that the ride was so bad they wanted to get down. No one will ever know if that was in the captain's mind.

[oggers]

Here's one. Transport Canada AIM RAC 9.3.

A clearance for an approach may not include any intermediate altitude restrictions. The pilot may receive this clearance while the aircraft is still a considerable distance from the airport, in either a radar or non-radar environment. In these cases, the pilot may descend, at his/her convenience, to whichever is the lowest of the following IFR altitudes applicable to the position of the aircraft:

(a) minimum en route altitude (MEA);

(b) published transition or feeder route altitude;

(c) minimum sector altitude (MSA) specified on the appropriate instrument approach chart;

(d) safe altitude 100 NM specified on the appropriate instrument approach chart;
or

(e) when in airspace for which the Minister has not specified a higher minimum, an altitude of at least 1 000 ft above the highest obstacle within a horizontal radius of 5 NM (1 500 ft or 2 000 ft within designated mountainous regions, depending on the zone) from the established position of the aircraft.

Doesn't get much clearer than that

That is what happens during own navigation from the en-route phase. That does not say you can leave your assigned altitude before established whilst being vectored to final.

The OP's question was specifically: can you leave assigned altitude whilst on a vector to final before becoming established. In the USA it is absolutely clear that you cannot. There is still no reference here to indicate it is legitimate to do so anywhere else.

Whilst being vectored ATC are responsible for terrain clearance. The changeover of responsibility back to pilot occurs not when you are cleared for the approach but when you hear the key words "resume own navigation". In the case of vectors to final (the case in point) you are not told to resume own nav but it stands to reason the point you resume responsibility for terrain avoidance is when established.

I am no longer surprised that the FAA have to spell this out every time a pilot is vectored to the ILS.

[aterpster]

oggers:

I am no longer surprised that the FAA have to spell this out every time a pilot is vectored to the ILS.

That is not the case. The regulations and related policy guidance were significantly changed in 1975 as a result of the 1974 TWA 514 CFIT.

That was 41 years ago. Everyone figured out what the 41 year old regulatory change meant.

[oggers]

...my point is that because of that accident you are reminded to "maintain [assigned altitude] until established" when you are vectored to intercept the localiser. As opposed to assuming you will maintain it. This thread has convinced me that is a wise move by the FAA.