Instruments Procedures

[funkypilot]

Hi everybody,

I have a few questions on the way procedures are designed.

1. I've read with interest the lot of discussions about MSA but can't find a final answer, that is to say: is it legal to fly at the MSA once we're inside the 25 NM radius according to PANS-OPS? It seems to me that yes

2. What are the criteria that make that a base turn is sometimes preferred to a procedure turn in reversal procedure and vice versa? I can't find the rationale for that in PANS-OPS.

3. Similarly, what are the criteria that make that a racetrack procedure is sometimes preferred to a reversal procedure and vice-versa?

4. Are any reversal and racetrack procedures protected for any entry, or only for direct entries? If the answer is that it is protected for any entry, it means that it is possible to enter a racetrack or reversal procedurefrom an omnidirectionnal arrival, even an offset or parallel entry?

It is a lot of questions I know, but i hate not understanding the reasons why things are done....

Thanks a lot for your answers / highlights !

FP

[funkypilot]

Ok, I think I answered by myself to question 4...

I understood from a more detailed reading of PANS-OPS that racetrack are protected for all types of entries as holding patterns are, but that it is possible to combine a racetrack with a higher holding pattern forcing the aircraft to arrive direct into the racetrack.

As for reversal procedure, I understood that there are only protected for a +30/-30 entry from the outbound leg, that can be extended to the virtual continuation of the inbound leg. The entry can also be restricted to a the outbound heading using a symmetrical holding pattern.

Someone can confirm?

[sevenstrokeroll]

flying at MSA...MSA is for emergency use only...otherwise, in absence of proper radar vectors, you should either be:

on a published portion of the approach, or a published feeder route with alitude listed.

IF you have an RNAV chart, you might have the Minimum Off Route Altitude for a lat long Grid and you might use that altitude, provided you know which grid you are in .

all in all, follow published procedures to the letter.

now, one might do a 90/270 course reversal on the same side as a published procedure turn.

and you must do a racetrack/holding pattern in lieu of procedure turn when it is published, IE 1 min from OM.

[funkypilot]

Thanks for your answers.

Maybe I wasn't clear enough regarding my question on whether using racetrack or reversal procedure, and using base turn or procedure turn with a reversal procedure:

I was looking at charts from a designer point of view and asking me: well, basically, racetrack and reversal, whether using base or procedure turn, have the same goal which is bringing the aircraft at the desired track and altitude.

So I was wondering why a procedure designer would rather choose a racetrack than a reversal, and if he/she chooses a reversal, what will make him/her decide to use a base or a procedure turn...

Difficult to explain... Hope someone followed me...

[minimumunstick]

flying at MSA...MSA is for emergency use only...

Not true. Earlier it was in the definition of MSA that it should only be used for emergency purposes, but this is taken out of the definition, and some companies will allow you to navigate freely within MSA to position yourself for the approach.

So formally it is legal, as long as you comply with ATC instructions/clearances of course.

[9.G]

3.2 TYPES OF MANOEUVRES

3.2.1 Where no suitable IAF or IF is available to construct the instrument procedure in the form shown in Figure I-4-3-1, a reversal procedure, racetrack or holding pattern is required.

NOTE: Racetrack procedures are used where sufficient distance is not available in a straight segment to accommodate the required loss of altitude and when entry into a reversal procedure is not practical. They may also be specified as alternatives to reversal procedures to increase operational flexibility (in this case, they are not necessarily published separately).

[sevenstrokeroll]

MSA may not give you radio nav...just terrain clearance

regarding RACETRACK...be advised you can do a regular procedure turn if a procedure turn is published...but you must use a racetrack if it is published inorder to stay within safe distance of fix.

if a procedure turn is published, you could conceivable use a racetrack to turn around...provided you are on the same side as the procedure turn

[ImbracableCrunk]

Seven,


Are you basing your answer on FAA/TERPS or PAN-OPS?

Gladly, this is a very international forum.

[aterpster]

minimumunstick:

Not true. Earlier it was in the definition of MSA that it should only be used for emergency purposes, but this is taken out of the definition, and some companies will allow you to navigate freely within MSA to position yourself for the approach.

MSAs are operational altitudes in PANS-OPS. They are not in the U.S. under TERPs. Canada uses TERPs, but I believe (not sure, though) they design their MSAs to be operational. In the U.S., MSAs on RNAV IAPs are not sectorized, making them useless even for emergency purposes in mountainous areas.

Look at the MSA on this one:

http://aeronav.faa.gov/d-tpp/1102/06941R18.PDF

[9.G]

MINIMUM SAFE ALTITUDE (MSA)
Altitude depicted on an instrument approach chart and identified as the minimum safe altitude which provides 1000 feet of obstacle clearance within a 25 NM radius from the navigational facility upon which the MSA is predicated. If the radius limit is other than 25 NM, it is stated. This altitude is for EMERGENCY USE ONLY and does not necessarily guarantee navaid reception. When the MSA is divided into sectors, with each sector a different altitude, the altitudes in these sectors are referred to as “minimum sector altitudes”.

MINIMUM SECTOR ALTITUDE (MSA) (ICAO)
The lowest altitude that may be used under emergency conditions that provides a minimum clearance of 300 meters (1000 feet) above all obstacles within a sector of a circle of 46 kilometers (25 NM) centered on a navigational aid.

ICAO and FAA are the same.

[aterpster]

9.G:

What version of MSFS do you fly?

[9.G]

aterpster, it's the same like for the most of us called Jeppesen, if that's what you're referring to. BTW in your example MSA is predicated on the RNAV way point RW 18 therefore it's not sectored and logically it can't be it's not a nav aid after all. Yet MSA is quite useful if you simply climb to MSA regardless of your position as long as you're within 25 NM and above MSA you're good.

[BOAC]

9.G - what is your reference for the ICAO def of Minimum Sector Altitude?

[9.G]

Jeppesen, Manual Text, main volume, section-chart glossary.

Same definition under ATC chapter ICAO definitions.

[funkypilot]

Thanks for answers.

9.G, it seems to me that your Jeppesen extract is not equivalent to ICAO? In Doc 81/68 PANS-OPS Volume II, the definition is just the same without "under emergency conditions". (ok I got the Fifth Edition 2006, maybe some things have changed since...)

BTW, your quote of PANS-OPS about racetrack is interesting, but I was precisely disturbed because of this;

- what is your understanding of "entry into a reversal is not practical"?
- what is your understanding of "increase operational flexibility"?

And any idea about using procedure turn rather than base turn or vice versa?

[9.G]

funkypilot, I use online Jeppesen and it's certainly most up to date revision.
4 SEP 09

© Jeppesen, 1999, 2009. All Rights Reserved.

AWM

AIR TRAFFIC CONTROL

International Civil Aviation Organization -- Definitions

Definitions in this listing are extracted from the following ICAO documents:

ICAO RULES OF THE AIR, ANNEX 2

PROCEDURES FOR AIR NAVIGATION SERVICES — AIR TRAFFIC MANAGEMENT, PANS-ATM (Doc 4444)

PROCEDURES FOR AIR NAVIGATION SERVICES — AIRCRAFT OPERATIONS, PANS-OPS (Doc 8168)

[9.G]

- what is your understanding of "entry into a reversal is not practical"?
- what is your understanding of "increase operational flexibility"?

Well, I think the key to the riddle is in that little note:
when is the entry into reversal not practical- it's when you come outside the cone of 30 degrees of the centerline, in this case you initially need to enter the holding before you commence the reversal procedure. I think, in this case racetrack is more useful and does increase operational flexibility. I stand to be corrected though.

[BOAC]

Well, we differ! The latest on-line Jepp ATC section that I can find has NO mention of "under emergency conditions" (page 4/ 1.2.5 Minimum Sector Altitude) and as funky says, nor does 8168. Do you have a newer copy?

[9.G]

Minimum safe altitude is FAA definition containing for EMERGENCY USE ONLY

Minimum sector altitude is ICAO definition without referring to emergency use.

I beg a pardon I was looking into the chart glossary as it contains both.

[aterpster]

9.G

aterpster, it's the same like for the most of us called Jeppesen, if that's what you're referring to. BTW in your example MSA is predicated on the RNAV way point RW 18 therefore it's not sectored and logically it can't be it's not a nav aid after all. Yet MSA is quite useful if you simply climb to MSA regardless of your position as long as you're within 25 NM and above MSA you're good.

The history of MSAs evolved from the military in the days of lousy nav aids and a method to recover from disorientation without flying into a mountain while inbound to an airport (air base). I have never heard of it as an altitude to be used to climb to in the event of a loss of GPS.

Let's say I suffer a loss of GPS at F70 at MDA and at the MAP. First, I have some significant terrain to the SE although the MSA controlling obstacle is well to the NE. And, to get to 12,100 from MDA within 25 miles I must make good a climb gradient of approximately 410 feet per mile, or 6.73%. In the process I hope I don't hit lesser, but nonetheless, potentially fatal terrain.

Not a pleasant prospect unless I am flying a really high-performance jet; one that well exceeds the minimum climb performance requirements.

Or I could tune in a local VOR and figure out a much lower safe altitude than 12,100.