I-09 Questions

Questions and comments about the PE Pilot Training Program

I-09 Questions

Postby Mark Hargrove » Mon Feb 20, 2012 12:25 am

I have a few questions about the I-09 rating (and about profile descents in general):

First, is ATC responsible for figuring out about roughly how long it will take for a particular aircraft (based on it's type) to descend from its enroute altitude to a lower altitude to meet a crossing restriction? In this case, I'm thinking specifically about GRAMM intersection on the KLAX RIIVR2 approach. It has a crossing restriction of "between FL210 and 17000". On the tutorial video Keith said to expect to cross it at FL190 or FL180 depending on the weather (and indeed, on the wonderful long videos of him "working" the arrival during the PE beta, he was instructing pilots to "cross GRAMM at, maintain FL190"). So how does that work? Should I restrict my filed enroute altitude from KLAS to something reasonably low (like FL260 or FL280) to make it easier for ATC to descend me to GRAMM, or do I file whatever I want, trusting ATC will start my descent in time to meet the restriction?

Second, after RIIVR intersection (heading to LAX 25L), the sequence of checkpoints occur at just about the right spacing to permit a constant rate descent down to 5000 at GAATE -- except for that weird "flat spot" between LUVYN and KRAIN. It's really no problem to deal with it, but I'm curious about its purpose -- why didn't the FAA just make LUVYN 11000 to allow a continuous descent from RIIVR?

Finally (and I really think this is asked and answered from a question I posted a few weeks ago about the I-05 rating, but I wanted to double-check), the fastest airplane I'm comfortable flying is the Citation Mustang. The Mustang's Vne is only 250 knots. That technically means I cannot file the RIIVR2 arrival because I cannot meeting the "at 280K" crossing restriction at GRAMM. For the rating, can I tell the controller that I'm unable to meet the speed crossing restriction and request that it be deleted? --or do I need to wait to fly the rating until I can become proficient in a faster airplane?

Thanks!

-M.
Mark Hargrove
Longmont, CO
PE: N757SL (Cessna 182T 'Skylane'), N757SM (Cessna 337 'Skymaster'), N757BD (Beech Duke Turbine)
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Re: I-09 Questions

Postby Keith Smith » Mon Feb 20, 2012 2:50 pm

Mark Hargrove wrote:I have a few questions about the I-09 rating (and about profile descents in general):

First, is ATC responsible for figuring out about roughly how long it will take for a particular aircraft (based on it's type) to descend from its enroute altitude to a lower altitude to meet a crossing restriction? In this case, I'm thinking specifically about GRAMM intersection on the KLAX RIIVR2 approach. It has a crossing restriction of "between FL210 and 17000". On the tutorial video Keith said to expect to cross it at FL190 or FL180 depending on the weather (and indeed, on the wonderful long videos of him "working" the arrival during the PE beta, he was instructing pilots to "cross GRAMM at, maintain FL190"). So how does that work? Should I restrict my filed enroute altitude from KLAS to something reasonably low (like FL260 or FL280) to make it easier for ATC to descend me to GRAMM, or do I file whatever I want, trusting ATC will start my descent in time to meet the restriction?


File whatever flight level is optimal for your aircraft based on the conditions and the length of flight. ATC doesn't calculate your top of descent, they'll issue the crossing restriction as soon as practical based on the confines of their airspace and surrounding traffic. If you pass your top of descent point and haven't been issued a lower altitude, you should request lower from the controller.

Second, after RIIVR intersection (heading to LAX 25L), the sequence of checkpoints occur at just about the right spacing to permit a constant rate descent down to 5000 at GAATE -- except for that weird "flat spot" between LUVYN and KRAIN. It's really no problem to deal with it, but I'm curious about its purpose -- why didn't the FAA just make LUVYN 11000 to allow a continuous descent from RIIVR?


It's not a flat spot, those are minimum altitudes, not mandatory altitudes. They don't want you below 10k, but you can certainly be above it.

Finally (and I really think this is asked and answered from a question I posted a few weeks ago about the I-05 rating, but I wanted to double-check), the fastest airplane I'm comfortable flying is the Citation Mustang. The Mustang's Vne is only 250 knots. That technically means I cannot file the RIIVR2 arrival because I cannot meeting the "at 280K" crossing restriction at GRAMM. For the rating, can I tell the controller that I'm unable to meet the speed crossing restriction and request that it be deleted? --or do I need to wait to fly the rating until I can become proficient in a faster airplane?


Yes, no change from the I-5 response, it's an identical situation. I have no idea if you can file it in the real word if you can't make the restriction, but the goal of the rating is to see if you can fly the STAR with its lateral and vertical guidance, we're less interested in the speed aspect, so feel free to file it and just advise the center controller that you're unable to meet the published speed restriction.
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Re: I-09 Questions

Postby Mark Hargrove » Mon Feb 20, 2012 5:23 pm

File whatever flight level is optimal for your aircraft based on the conditions and the length of flight. ATC doesn't calculate your top of descent, they'll issue the crossing restriction as soon as practical based on the confines of their airspace and surrounding traffic. If you pass your top of descent point and haven't been issued a lower altitude, you should request lower from the controller.

Ah, this makes total sense! As a passenger on United I've listened to pilots request higher and lower altitudes many, many times -- but it was always to try to find a more comfortable "ride" for the passengers. I hadn't considered using a request for a lower altitude to make a crossing restriction.

It's not a flat spot, those are minimum altitudes, not mandatory altitudes. They don't want you below 10k, but you can certainly be above it.

<Embarrassed Facepalm>I don't know how I overlook obvious things like this!

Thanks for the guidance on the speed restriction -- I thought that would be the answer but wanted to double-check.

-M.
Mark Hargrove
Longmont, CO
PE: N757SL (Cessna 182T 'Skylane'), N757SM (Cessna 337 'Skymaster'), N757BD (Beech Duke Turbine)
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Re: I-09 Questions

Postby arb65912 » Wed Feb 29, 2012 1:24 pm

File whatever flight level is optimal for your aircraft based on the conditions and the length of flight. ATC doesn't calculate your top of descent, they'll issue the crossing restriction as soon as practical based on the confines of their airspace and surrounding traffic. If you pass your top of descent point and haven't been issued a lower altitude, you should request lower from the controller.


TOD, could anybody point out the reference to calculate it? I do not do long IFR flights, they are boring. :lol:
On the other hand, I would like to know how to calculate TOD if I needed to.

Thank you, Cheers, Andrzej

BTW, I flew I-09 last night and had no problems with altitude but .... I filed very low one FL220 for the reasons mentioned above. :)
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Re: I-09 Questions

Postby Keith Smith » Wed Feb 29, 2012 1:58 pm

AJ, it's math that you're going to want to start practicing in your head. How much altitude to lose, and how quickly will you descend? From that, you get a "time required to complete descent".

Once you have that figure, you can work out how much distance you'll cover during that time by considering your average ground speed.

Give it some thought, don't rush. It's an important concept for flight planning and it's something you'll eventually need to be able to calculate while flying an airplane on a cross country flight.
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Re: I-09 Questions

Postby arb65912 » Wed Feb 29, 2012 3:13 pm

Thank you, Keith. I will start practicing right away. We are talking just a rough estimates, I assume. Cheers, AJ.
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Re: I-09 Questions

Postby Mark Hargrove » Wed Feb 29, 2012 10:40 pm

The two-step rule-of-thumb I have memorized is:

"Altitude to descend" * 3 / 1000 = # of miles from TOD to BOD (in NM)
and
Ground speed * 5 = necessary descent rate (in FPM)

Say we're level at FL210 with a ground speed of 300 KT and want to descend to 11,000':

Descent distance = FL210 - 11,000 = 10,000 * 3 = 30,000 / 1000 = 30nm
and
descent rate = 300 * 5 = 1500 FPM

So at 30nm from our desired BOD we start a descent at 1500FPM.

I've learned to add 5 miles or so the calculated TOD point to make sure I make my crossing restrictions (oh, and keep your airspeed under control during the descent or it messes up the calculation). I also have to admit that flying a glass cockpit (like the Garmin G1000 in the Citation Mustang) has spoiled me: I look at the flight plan in the GPS to see the time remaining to the waypoint that represents my BOD (which is displayed in minutes remaining), then wait until I'm the right number of minutes away to start a 2000 FPM descent (or 1000 FPM, or whatever).

All of this is just a couple of practical ways of doing what Keith said in his post: how far and how fast do you want to descend vertically, and how far will the airplane travel horizontally while you're doing that descent?

-M.
Mark Hargrove
Longmont, CO
PE: N757SL (Cessna 182T 'Skylane'), N757SM (Cessna 337 'Skymaster'), N757BD (Beech Duke Turbine)
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Re: I-09 Questions

Postby arb65912 » Thu Mar 01, 2012 5:45 am

Thank you , Mark.

I knew about the *3 rule but I knew it even in a simpler form, you just take the altitude difference you want to descend in thousands of feet, saves the division by 1000.

In your example : 21,000 - 11,000 = 10 ( thousand) 10*3 =30 NM .

I will remember the sped rule GS * 5.

I assume that with GS calculated that way, *3 rule for distance will be correct.

Thank you again.

PE is the best source of real life navigation information.

Cheers, AJ
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