Min altitude during a procedure turn

[Whirlwind]

I'm having the hardest time finding this, so hopefully someone can help...

"What is the altitude margin of error while on a procedure turn during an instrument approach?"

I'm not asking in relation to a checkride, rather what is the allowed margin of error in everyday flying, Part 91. Is there a difference if the airplane is Part 25 rather than Part 23?

I need a source because neither myself nor my captain can find anything written down regarding what altitude must be maintained on a published segment of the approach such as a procedure turn.

Thanks...

 

[minitour]

Well...I don't have any references to point to but here's my feelings/thoughts:

The IAP is there to make sure you don't hit anything on your way to the runway/runway environment. With that in mind, I think the altitude shown (being a minimum altitude) should be your minimum altitude. Don't go below it.

If you go under by 50' you might be okay in most cases, but I think you'd want to nail it more often than not.

Not sure on the 23 v 25 thing. Good luck!

-mini

 

[Whirlwind]

Well...I don't have any references to point to but here's my feelings/thoughts:

The IAP is there to make sure you don't hit anything on your way to the runway/runway environment. With that in mind, I think the altitude shown (being a minimum altitude) should be your minimum altitude. Don't go below it.

I personally make it a point not to descend below the published altitudes, but in this case the question arose during a PPE ride.

So in this case, what rule applies when an FAA inspector is sitting behind you during the flight? If you go 20 feet below the altitude published on the chart, can he bust you for that? If so, where is that written?

Not sure on the 23 v 25 thing. Good luck!

I asked about the 23/25 thing because I thought perhaps the rules might be different for transport catagory airplanes. I can't find anything in the FAR/AIM either way however...

 

[philo beddoe]

I'm not exactly sure what you are asking, but here goes:

IAP course reversals, which include procedure turns, racetrack entries and teardrop entries (fairly rare) all have 1000' of clearance above the controlling obstacle, rounded to the nearest 100'.

The are for a PT is approximately 4nm on the non-turn side of the PT and 6-8 niles on the PT side.

They survey the tallest obstacle n that area and tack on 1000'.

If you manage to kill yourself on the PT, you are very, very lost.


If I remember right, IFR PTS is +/-100ft on all altitudes except minimums.

 

[Flying Illini]

If you go under by 50' you might be okay in most cases, but I think you'd want to nail it more often than not. -mini

I don't have any references for you, nor do I have the answer to your question but here is something to keep in mind.
Your altimeter can have up to a 75' error. Couple that with dipping slightly below the minimum altitude for that segment of the approach and all of a sudden you could be 125' low instead of 50' low. From what Philloe posted, that doesn't look like it would be a problem on the PT but it becomes much more significant the lower your altitude and the closer you get to the airport on the approach.

 

[minitour]

Your altimeter can have up to a 75' error.

Good call!

I never thought about instrument errors n such.

Yep, I'm gonna stick to staying at or above the PT altitude...

-mini

 

[Wiggums]

IAP course reversals, which include procedure turns, racetrack entries and teardrop entries (fairly rare) all have 1000' of clearance above the controlling obstacle, rounded to the nearest 100'.

The are for a PT is approximately 4nm on the non-turn side of the PT and 6-8 niles on the PT side.

The document you are looking for is called the UNITED STATES STANDARD FOR TERMINAL INSTRUMENT PROCEDURES, or TERPS. I've included a link for you at end of this post, see page 12-1. The above is correct you will have atleast 1000' of clearance during the IAP segment. The safe area is a little more complicated, but the above posters rule of thumb is reasonable, assuming there are CAT B or higher mins for the approach. So you do get to be what seems to be quite a large margin of safety. However, don't forget to consider that at 180kts and 25 deg your turn radius is 6170ft, so the bottom of your entry will take you atleast 2nm away from the course centerline. Good reason to fly right on the radial and make nice turns.

http://www.e-publishing.af.mil/pubfiles/af/11/afman11-226/afman11-226.pdf

 

[Whirlwind]

Thanks all for the replies...

Yes, I'm aware of the instrument PTS standards, but that isn't what I had in mind in this case. Thankfully those are pretty clear, at least as far as government documents go.

I was looking for the rules related to flying in general, mostly because if a FAA inspector wants to make a bust on being 20' below the published number on a PT, then I want to know on what basis that would be, and what defense to it might exist.

Thankfully in this case no bust happened, but I'd still like to know the answer.

Thanks...

 

[Singlecoil]

I'm not exactly sure what you are asking, but here goes:

IAP course reversals, which include procedure turns, racetrack entries and teardrop entries (fairly rare) all have 1000' of clearance above the controlling obstacle, rounded to the nearest 100'.

The are for a PT is approximately 4nm on the non-turn side of the PT and 6-8 niles on the PT side.

They survey the tallest obstacle n that area and tack on 1000'.

If you manage to kill yourself on the PT, you are very, very lost.


If I remember right, IFR PTS is +/-100ft on all altitudes except minimums.

I hate to bring this up again, but here goes: Don't forget that your altimeter is lying to you if the temperature is different than standard temp. The AIM tells you to apply a correction when the temperature is colder than standard. On a cold day you could be lower than indicated by 500 feet or more. Not a big deal in North Dakota, but a huge deal in Montana or Alaska when flying near mountains.
The procedure turn area is where the error can be the greatest. The higher you are above the reporting station, the greater the error. Something to think about on a dark night or when in IMC.

 

[Whirlwind]

I hate to bring this up again, but here goes: Don't forget that your altimeter is lying to you if the temperature is different than standard temp.

That's all well and good for standard altimeters, but if memory serves, the air data computers in our cockpit correct for this on our digital altimeters...

If I'm mistaken, someone need only point it out to me...