DocLightning
Topic Author
Posts: 20246
Joined: Wed Nov 16, 2005 8:51 am

### Why Are Holding Patterns Oval?

Why not just have the aircraft fly in a circle?

Sorry, this sort of thing occurs to my bored brain on cold, wet Saturday evenings.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan

akiss20
Posts: 827
Joined: Tue Sep 04, 2007 9:50 am

### RE: Why Are Holding Patterns Oval?

 Quoting DocLightning (Thread starter):Why not just have the aircraft fly in a circle? Sorry, this sort of thing occurs to my bored brain on cold, wet Saturday evenings.

How would you know if you are keeping the fix centered/your radius is good? (Also constant banking is annoying as hell to maintain accurately)
Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are

DocLightning
Topic Author
Posts: 20246
Joined: Wed Nov 16, 2005 8:51 am

### RE: Why Are Holding Patterns Oval?

 Quoting AKiss20 (Reply 1): How would you know if you are keeping the fix centered/your radius is good?

I dunno. Why would flying in a circle preclude that?

Dammit, Jim, I'm a doctor, not an airman!
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan

swiftski
Posts: 1837
Joined: Tue Dec 19, 2006 6:19 am

### RE: Why Are Holding Patterns Oval?

 Quoting DocLightning (Reply 2):I dunno. Why would flying in a circle preclude that?

The pattern as it is works well. Flying overhead the fix, then making rate one turns, timing the outbound leg and tracking a bearing/radial inbound allows you to actually be quite accurate. Also, as pointed out, there is less time spent in the turn than if the pattern was a circle.

Alias1024
Posts: 2262
Joined: Mon Oct 25, 2004 11:13 am

### RE: Why Are Holding Patterns Oval?

 Quoting DocLightning (Thread starter):Why not just have the aircraft fly in a circle? Sorry, this sort of thing occurs to my bored brain on cold, wet Saturday evenings.

Wind

If you maintained a constant bank angle for the turn your circles would be pushed downwind. The whole idea of a holding pattern is to keep you in one area.
It is a mistake to think you can solve any major problems with just potatoes.

SAAFNAV
Posts: 390
Joined: Wed Mar 17, 2010 5:41 pm

### RE: Why Are Holding Patterns Oval?

Also, Holds are based on Rate 1 turns, meaning 1 180 turn takes 1 minute. Below Fl145, you go straight for 1 minute, and turn inbound again for another minute, and home on the radial for another minute. That gives you 4 minutes to complete one hold.

The above is for Still Air Conditions. We use a Rule-of-Thumb: for every 10Kts Tailwind Component on the Inbound leg, you add 10sec on the outbound leg, so as to keep the whole pattern at 4 minutes.

So when ATC gives you an Estimated Approach Time, you can play around with the timings so that you can be overhead the fix and continue with the Approach to within a few seconds.

Hopes this helps.

Erich
L-382 Loadmaster; ex C-130B Navigator

SAAFNAV
Posts: 390
Joined: Wed Mar 17, 2010 5:41 pm

### RE: Why Are Holding Patterns Oval?

 Quoting DocLightning (Reply 2): I dunno. Why would flying in a circle preclude that?

If you have very strong Crosswinds, the wind would squash your circle.

Longer legs gives you opportunity for straighten it out.
L-382 Loadmaster; ex C-130B Navigator

Vmcavmcg
Posts: 78
Joined: Wed Sep 15, 2010 11:52 am

### RE: Why Are Holding Patterns Oval?

 Quoting SAAFNAV (Reply 5):and home on the radial for another minute

Not to nit pick, but you don't home you track in on the radial if you are holding over a VOR and track the bearing if you are holding over an NDB.

As everyone said, the purpose of holding is to position your self over a specific point. If you had winds and held in a circle, then at some point in time you would not be able to maintain the point as you would not be able to bank steep enough to compensate for the winds. In reality you would have an oval holding pattern.
If we weren't all crazy, we would go insane!

SAAFNAV
Posts: 390
Joined: Wed Mar 17, 2010 5:41 pm

### RE: Why Are Holding Patterns Oval?

 Quoting Vmcavmcg (Reply 7): Not to nit pick, but you don't home you track in on the radial if you are holding over a VOR and track the bearing if you are holding over an NDB.

Yep, technically that is correct, but if you use the 'tail' of the RMI for both, it is pretty much the same thing.
Different terminology, but in essence you use it the same.

Regards,

Erich
L-382 Loadmaster; ex C-130B Navigator

sfotom
Posts: 26
Joined: Fri Sep 04, 2009 9:50 pm

### RE: Why Are Holding Patterns Oval?

Aircraft attitude gyros knowledge of "up" and "down" gradually drifts with time. There is a very gentle correction system within the gyro that resets it to vertical based on the pull of gravity. The correction system of a attitude gyro is gentle (slow) enough that it is normally not affected by the aircraft maneuvering, however if an aircraft was to enter a constant bank for an extended time the gyro would begin loose it's correct reference to "up" and "down". Instrument holding patterns are "racetrack" in shape so that this does not happen.

Quokka
Posts: 1315
Joined: Fri Sep 03, 2010 12:26 pm

### RE: Why Are Holding Patterns Oval?

A related question: would the "shape" of the oval vary according to the airport that is being approached( sometimes longer, sometimes shorter). I have in mind approaches to airports that are in close proximity to another one, for example LHR and LGW, or are the holding areas sufficiently far enough apart to avoid overlap?

Pihero
Posts: 4248
Joined: Mon Jan 31, 2005 5:11 am

### RE: Why Are Holding Patterns Oval?

First of all, the shape of a holding pattern is not oval, it is as sfotom in the shape of a race track : one 180° turn in one direction, followed by an "outbound straight leg and then back to the departure point through another 180° turn and an inbound leg to the origin.
That's in theory and with no wind.
The wind is going to mess everything up and the pattern will be misshaped, but just understand that if one doesn't correct for wind, at the end of the inboud leg, one would found oneself having to "clim back up-wind " to reach the origin of the hold.
That remark was at the beginning of a few holdong correction techniques, one in particular is to steer outbound with triple the drift angle for that leg....etc...

 Quoting SAAFNAV (Reply 5):Holds are based on Rate 1 turns,

Correct for slow airplanes... but that rate one, worth around 15° of bank per 100Kt TAS is not very comfortable for jets that hold at 210kt +. We know expect the bank at 25° for comfort. The speed for which the pattern has been designed for is on the AIPs.

 Quoting SAAFNAV (Reply 6):If you have very strong Crosswinds, the wind would squash your circle.

Coprrect again, but it does everything, doesn't it ?
The reason for not flying circles are about 1) Fuel consumption as the load factor in the turn forces a thrust increase and 2) passenger comfort.

Of course all the above is totally moot with an advanced EFCS/AP system, which flies a pattern quite nicely. Fun to watch, but with some strong winds, it also have to adapt with potatoid racetrack patterns.
Contrail designer

ThrottleHold
Posts: 546
Joined: Tue Jul 18, 2006 11:00 pm

### RE: Why Are Holding Patterns Oval?

Fkying in a turn at a constant altitude burns more fuel. That's why you will hear crews requesting longer outbounds than published. I personally requested, and was approved, 50nm legs holding for JFK one wintery night.

xero9
Posts: 124
Joined: Thu Feb 22, 2007 3:12 am

### RE: Why Are Holding Patterns Oval?

While this likely has nothing to do with it, imagine anyone who is nervous about flying being in a constant turn for say 20 minutes?

But about the winds.. I have a question. If the winds are say from 270, would the long stretch be from east west? And if the winds are say from 180, the long stretch would be from north south? Just curious.

Pihero
Posts: 4248
Joined: Mon Jan 31, 2005 5:11 am

### RE: Why Are Holding Patterns Oval?

 Quoting xero9 (Reply 13):If the winds are say from 270, would the long stretch be from east west? And if the winds are say from 180, the long stretch would be from north south? Just curious.

The holds are well defined, both as to the inbound radial/bearing and the direction of the turns. the aircrews have to cope with the actual wind conditions.
Contrail designer

tb727
Posts: 1854
Joined: Thu Jun 30, 2005 1:40 pm

### RE: Why Are Holding Patterns Oval?

 Quoting Alias1024 (Reply 4): Wind If you maintained a constant bank angle for the turn your circles would be pushed downwind. The whole idea of a holding pattern is to keep you in one area.

Yeah, it's crazy how far you get pushed if you just do circles even down low. I was out with a Captain upgrade trainee west of Detroit working on his steep turns before his checkride and just kept doing 360 after 360 and we ended up drifting about 15 miles, then we would fly a straight line back to the SW into the wind and start over again. The track didn't show up on flightaware though, it would have been a great visualization.
Too lazy to work, too scared to steal!

oly720man
Posts: 5771
Joined: Fri May 21, 2004 7:13 am

### RE: Why Are Holding Patterns Oval?

 Quoting Quokka (Reply 10):A related question: would the "shape" of the oval vary according to the airport that is being approached( sometimes longer, sometimes shorter). I have in mind approaches to airports that are in close proximity to another one, for example LHR and LGW, or are the holding areas sufficiently far enough apart to avoid overlap?

To see it in action, go here

http://casper.frontier.nl/egkk/

and set the date/time to Friday 26th November 06:00 and set the speed to 25x. Click the show tracks box to see the flightpaths. Screenshot here

There are 3 holds for LHR as can be seen by the racetracks, NW, NE and SE of London. The nearest one to LGW (runway indicated by the white line, centre bottom) has the planes at around 11000ft, rather higher than the aircraft approaching LGW. As far as I know the hold(s) for LGW are south of LGW.

Planes generally fly the oval but there's an occasional 360, presumably for shorter spacing.
wheat and dairy can screw up your brain

Pihero
Posts: 4248
Joined: Mon Jan 31, 2005 5:11 am

### RE: Why Are Holding Patterns Oval?

Why not look at the official STAR charts for both Heathrow and Gatwick ?
Here is the LHR South-East arrival procedure ;
STAR Biggin
and the East/South-East STAR chart for LGW :
STAR Timba
You have a few examples of defined arrival holding stacks.

 Quoting oly720man (Reply 16):there's an occasional 360, presumably for shorter spacing.

It's generally an interrupted hold for spacing, and it could be a continuous turn toward the approach path.

Btw, maps like the above have basically no meaning. One would need the official trajectories in order to understand the situation as close to reality as possible.

Spelling spelling spelling

[Edited 2010-11-29 16:32:59]
Contrail designer

pilotpip
Posts: 2824
Joined: Fri Sep 19, 2003 3:26 pm

### RE: Why Are Holding Patterns Oval?

 Quoting Pihero (Reply 11):The reason for not flying circles are about 1) Fuel consumption as the load factor in the turn forces a thrust increase

This perhaps more than anything. When we get holding instructions one of the first things we do is consult the performance charts, determine our max endurance airspeed and ask for it. If holding instructions are given we want to do everything we can to avoid diverting. Conserving as much fuel as possible leading up to and in the hold allows us to stretch the amount of time we are in the hold.
DMI

### Who is online

Users browsing this forum: No registered users and 12 guests

### Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos