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Question About Holding Patterns  
User currently offlineYokoTsuno From Singapore, joined Feb 2011, 348 posts, RR: 0
Posted (3 years 4 months 3 weeks 1 hour ago) and read 5500 times:

I just got back from Delhi, which is an ideal place to study holding patterns, especially domestic flights  

These holding patterns always seen to be rectangular with rounded corners in shape. Is this always the case or are there airports with different patterns?

16 replies: All unread, jump to last
 
User currently offlineRomeoMike From Canada, joined Nov 2005, 36 posts, RR: 0
Reply 1, posted (3 years 4 months 3 weeks 1 hour ago) and read 5486 times:

You're correct. Holds are a racetrack pattern, with both 'long' sides being 1 minute of flying in length, then a 1 minute, 180 degree turn at each end.

http://en.wikipedia.org/wiki/Holding_(aviation)

I don't believe there are non-standard holding shapes, but a hold can be either left or right turns, depending on the airspace/ATC requirements.

[Edited 2011-06-12 05:23:55]

User currently offlineNWADC9 From United States of America, joined May 2004, 4898 posts, RR: 10
Reply 2, posted (3 years 4 months 2 weeks 6 days 9 hours ago) and read 5336 times:

Holds are essentially elongated loops, like a racetrack. They can be at a NAVAID or an intersection formed by intersecting radials from two or more NAVAIDs or a DME fix along a radial.

To fly a hold, the pilot would essentially fly towards the fix, then once over it, start a 180 degree standard rate turn (three degrees per second, thus one minute) either left or right as directed by ATC or on a published chart (right is standard). Once the turn is completed, the aircraft should be abeam the fix, then the aircraft would maintain heading for one minute before doing another 180 turn to intercept the radial towards the fix. The goal is to make the inbound leg towards the fix one minute, so the outbound leg would be adjusted to make that happen. In the case of a DME hold, the aircraft would fly a certain distance instead of a one minute leg, thus alleviating this issue. In reality, a hold may be stretched out much further than one minute or the published distance, especially with airliners, to minimize the number of turns for passenger comfort.



Flying an aeroplane with only a single propeller to keep you in the air. Can you imagine that? -Capt. Picard
User currently offlineKELPkid From United States of America, joined Nov 2005, 6415 posts, RR: 3
Reply 3, posted (3 years 4 months 2 weeks 6 days 9 hours ago) and read 5331 times:

Quoting NWADC9 (Reply 2):
To fly a hold, the pilot would essentially fly towards the fix, then once over it, start a 180 degree standard rate turn (three degrees per second, thus one minute)

Although I know that in a GA plane, a 2 minute turn is standard rate, I seem to recall poking my head into (mostly museum pieces) early jet cockpits, and seeing a 4 minute turn coordinator on the panel...   I always assumed that that was because a 4 minute turn in a jet at cruise speed and altitude would be better for passenger comfort...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineKaiarahi From Canada, joined Jul 2009, 3039 posts, RR: 28
Reply 4, posted (3 years 4 months 2 weeks 3 days 21 hours ago) and read 4961 times:

Quoting KELPkid (Reply 3):
I always assumed that that was because a 4 minute turn in a jet at cruise speed and altitude would be better for passenger comfort...

I've never experienced a hold at cruise speed - manoeuvering speed or ATC-directed speed is more likely.

[Edited 2011-06-15 09:32:04]


Empty vessels make the most noise.
User currently offlineKELPkid From United States of America, joined Nov 2005, 6415 posts, RR: 3
Reply 5, posted (3 years 4 months 2 weeks 3 days 10 hours ago) and read 4844 times:

Quoting Kaiarahi (Reply 4):
I've never experienced a hold at cruise speed - manoeuvering speed or ATC-directed speed is more likely.

I'd love for an old-school jet pilot to tell us why many older jets had a 4-minute turn coordinator in the panel, though. I've seen references, too, to 4 minute standard rate turns in jets...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineMir From United States of America, joined Jan 2004, 21730 posts, RR: 55
Reply 6, posted (3 years 4 months 2 weeks 2 days 19 hours ago) and read 4750 times:

Quoting KELPkid (Reply 5):
I'd love for an old-school jet pilot to tell us why many older jets had a 4-minute turn coordinator in the panel, though. I've seen references, too, to 4 minute standard rate turns in jets...

The rough rule of thumb for a standard rate turn is use an angle of bank equal to 15% of the airspeed. At 200kts, that would mean 30 degrees of bank, which is pretty much the most you'd want to use with passengers aboard. And since most jets tend to fly faster than that unless on approach, using half-standard rate makes more sense from a passenger comfort perspective (not to mention the trouble you can get into in steep banks at high altitudes). It's not like the aim is to complete the holding pattern as quickly as possible, anyway.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlinejcxp15 From United States of America, joined Jun 2001, 997 posts, RR: 5
Reply 7, posted (3 years 4 months 2 weeks 2 days 13 hours ago) and read 4674 times:

Don't forget under ICAO rules, a standard hold is 1 minute on the outbound leg of the hold as opposed to the US standard of 1 minute inbound.

IMHO this is a better procedure and is much easier as it involves a lot less thought - you just time one minute outbound.


User currently offlineMir From United States of America, joined Jan 2004, 21730 posts, RR: 55
Reply 8, posted (3 years 4 months 2 weeks 2 days 9 hours ago) and read 4620 times:

Quoting jcxp15 (Reply 7):
Don't forget under ICAO rules, a standard hold is 1 minute on the outbound leg of the hold as opposed to the US standard of 1 minute inbound.

IMHO this is a better procedure and is much easier as it involves a lot less thought - you just time one minute outbound.

Yeah, but then how would examiners fail people on Instrument checkrides?   

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlinePolymerPlane From United States of America, joined May 2006, 991 posts, RR: 3
Reply 9, posted (3 years 4 months 2 weeks 2 days 7 hours ago) and read 4593 times:

For busy airport, how many holding points do they typically have? how do they deal with massive backlog, i.e. for bad weather,etc. and what happen if they ran out of holding points?


One day there will be 100% polymer plane
User currently offlineKELPkid From United States of America, joined Nov 2005, 6415 posts, RR: 3
Reply 10, posted (3 years 4 months 2 weeks 2 days 7 hours ago) and read 4588 times:

Quoting PolymerPlane (Reply 9):
For busy airport, how many holding points do they typically have? how do they deal with massive backlog, i.e. for bad weather,etc. and what happen if they ran out of holding points?

You can invent a hold on the fly at an intersection, GPS fix, over the navaid of your choice, or as published   The controllers can stack aircraft in the hold, too (with 1000' vertical sep). I have been #3 for the ILS at MMV (in actual IMC, nonetheless) holding at the MM locator outer marker in a Cessna. Once the seperation is there (next aircraft on the approach, far enough away from the holding pattern), they have everyone in the hold descend 1000'. They (ATC) changed the missed, though, as the missed approach has you fly the localizer back to the LOM and enter the same holding pattern. You got held at the nearby UBG VORTAC for the missed.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1655 posts, RR: 1
Reply 11, posted (3 years 4 months 2 weeks 2 days 6 hours ago) and read 4584 times:

We aren't subject to four course range intersections anymore, fan markers or NDBs. A controller can set up a hold at anyplace they damn well please in the sky and stack airplanes over that fix as they see fit. This happened, to some degree, on 9/11 when all flights were ordered to land and it proved to be no problem.

User currently offlineJD747 From Spain, joined Nov 2006, 47 posts, RR: 0
Reply 12, posted (3 years 4 months 2 weeks 2 days ago) and read 4513 times:

Quoting RomeoMike (Reply 1):

You're correct. Holds are a racetrack pattern, with both 'long' sides being 1 minute of flying in length, then a 1 minute, 180 degree turn at each end.

The 1 minute of flying rule applies when your are at or below FL140 or 14.000 ft. Above FL140 or 14.000 ft, is 1 minute and 30 seconds. Also, the length of the inbound or outbound can be define by a FIX, wich could be for example a VOR/DME/RADIAL. It's all defined in the ICAO document 8168 (section 6)

Regards.

[Edited 2011-06-17 05:41:44]

[Edited 2011-06-17 05:44:17]


Juan D.
User currently offlineYokoTsuno From Singapore, joined Feb 2011, 348 posts, RR: 0
Reply 13, posted (3 years 4 months 2 weeks 1 day 10 hours ago) and read 4421 times:

Quoting Mir (Reply 6):
At 200kts, that would mean 30 degrees of bank, which is pretty much the most you'd want to use with passengers aboard.
I still don't understand the reason why a racetrack shape is used. Wouldn't it be more comfortable for the passengers to just fly in a circle which I'd figure would only require very little and constant banking, hardly noticable.

Or is it hard for the pilots to maintain a circle?

Quoting KELPkid (Reply 10):
The controllers can stack aircraft in the hold, too (with 1000' vertical sep).
How tall can these stacks actually become?


User currently offlineNWADC9 From United States of America, joined May 2004, 4898 posts, RR: 10
Reply 14, posted (3 years 4 months 2 weeks 1 day 10 hours ago) and read 4408 times:

Quoting jcxp15 (Reply 7):
Don't forget under ICAO rules, a standard hold is 1 minute on the outbound leg of the hold as opposed to the US standard of 1 minute inbound.

Makes sense. No math, which is perfect for a phase of flight already as stressful as it is!

Quoting YokoTsuno (Reply 13):
I still don't understand the reason why a racetrack shape is used. Wouldn't it be more comfortable for the passengers to just fly in a circle which I'd figure would only require very little and constant banking, hardly noticable.

Or is it hard for the pilots to maintain a circle?

Doesn't give you enough time to correct for wind drift and track back to the fix.



Flying an aeroplane with only a single propeller to keep you in the air. Can you imagine that? -Capt. Picard
User currently offlineKELPkid From United States of America, joined Nov 2005, 6415 posts, RR: 3
Reply 15, posted (3 years 4 months 2 weeks 1 day 8 hours ago) and read 4384 times:

Quoting YokoTsuno (Reply 13):
How tall can these stacks actually become?

Depends...you can start at the next thousand foot altitude above the minimum vectoring altitude and go up from there. There could very well be airspace restrictions up higher (for example, a high altitude airway or a path for an apporach). I have seen 10 aircraft stacked in a hold over the BTG VORTAC (one of those clear days where contrails were being made at almost all altitudes...). The reason for the hold was severe fog at SEA that was necessitating CAT III approaches. PDX got lots of diversions that day  



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineMir From United States of America, joined Jan 2004, 21730 posts, RR: 55
Reply 16, posted (3 years 4 months 2 weeks 1 day 6 hours ago) and read 4373 times:

Quoting YokoTsuno (Reply 13):
Or is it hard for the pilots to maintain a circle?

Yes. Modern navigation equipment could probably do it fine, but some traditions die hard, and as long as people are learning to do racetracks with the old school navigation equipment, racetracks will stay.

Keep in mind that if you were to fly around at a constant bank, you would only make a circle if there was no wind. Any wind would push your ground track one way or the other, and you'd never get back to where you started. Thus, you would eventually drift out of the area in which ATC wants to keep you, without any real way of knowing where you were. Pilots do learn to track a constant circle over the ground during their basic training by varying bank angle throughout the turn, but this is predicated on being able to see the ground - since holding is an instrument procedure, the assumption is that you CAN'T see the ground, and thus you really have no way of knowing how much bank to use at any point. Thus, the racetrack pattern - it provides you with an inbound leg to make sure you stay where you need to stay, and allows for standard rate turns (or whatever maximum bank the airplane could use at its airspeed) to take the guesswork out of how much bank you need.

-Mir



7 billion, one nation, imagination...it's a beautiful day
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