Why do prop planes turn away from the runway so soon

Carawaystick · 20-08-2015 02:43PM #1

Over the last few years I noticed prop planes turn away from the runway centreline very soon after takeoff. I was travelling along the r132 at the end of runway 10 in Dublin the other day and I'd say the aer arran had turned 90 degrees before it had crossed my road.

Is it to avoid turbulance or they are going slower and to get out of the way sooner or what?

TheChizler · 20-08-2015 02:47PM

I think it's to do with them being quieter than jets. Jets have to maintain course until they reach a certain altitude before they can change course to fly over more populated areas (or maybe changing course means they gain altitude slower and they should be doing this as fast as possible for a while), and this altitude is less for props. I could be totally wrong...

Irish Steve · 20-08-2015 02:54PM

Noise is a factor, but the speed aspect is also in there, it clears the departure path for faster jets more rapidly, which with traffic levels the way they are at Dublin is a significant factor these days. ATR's climb speed is in the range 170 to 190 Kts, Jets will accelerate to 250 Kts, and faster above 10,000 Ft, (bird strike issues) so an ATR ahead of a jet will mean that one or the other has to be routed away from the normal profile to allow the jet to accelerate and climb at normal speeds. The normal separation requirement is 1000 Ft vertically or 5 Miles, so by turning the props away from the centreline departure route, the separation criteria are more rapidly met.

Growler!!! · 20-08-2015 03:27PM

Irish Steve is correct. The prop planes (Category A/B) will climb to 750ft and make a right turn to the DUB VOR on departure from runway 28. This is to facilitate the fact that they have less climb performance and have a slower ground speed (Indicated airspeed 160kts or 170kts depending on the ATR model) than jets.

A jet (Category C/D) departure will be straight ahead until passing the OE NDB about 5 miles from the runway end before turning.

EchoIndia · 20-08-2015 03:30PM

Here is an SID chart for non-jet departures off runway 28. Note the "Turn at 750ft QNH" notation.
http://www.iaa.ie/safe_reg/iaip/Published%20Files/AIP%20Files/AD/Chart%20Files/EIDW/EI_AD_2_EIDW_24-9_en.pdf

VG31 · 20-08-2015 04:57PM

I've noticed that the ATRs turn soon after takeoff (at 750ft QNH in the chart above) and fly over the city but the Dash 8s turn much later. Does anyone know why this is?

L1011 · 20-08-2015 05:16PM

Dash 8s are significantly faster, if that changes procedures again.

Lustrum · 20-08-2015 11:27PM

They do this on some of the SID's in Schipol too where you're climbing straight ahead for 5NM or so, if it's busy they'll turn you off early to make way for the next departure, particularly if they're not on the same departure as you

Teebor15 · 21-08-2015 07:33AM

The ATR 42/72 are Cat B whereas the Dash 8-400 (Flybe) are Cat C. Basically their faster.

Alaba320 · 21-08-2015 07:53AM

Growler!!! wrote: »

Irish Steve is correct. The prop planes (Category A/B) will climb to 750ft and make a right turn to the DUB VOR on departure from runway 28. This is to facilitate the fact that they have less climb performance and have a slower ground speed (Indicated airspeed 160kts or 170kts depending on the ATR model) than jets.

A jet (Category C/D) departure will be straight ahead until passing the OE NDB about 5 miles from the runway end before turning.

You can have prop aircraft in cat C and jets in cat B. Aircraft categories have nothing to do with what means of propulsion the aircraft has, it is based on speed of the aircraft (clean stall speed X 1.3)

I'm not familiar with the Dash 8, but this could be the reason the don't make the early turns. Also just to add confusion...a turboprop which usually lies in Cat B, could end up in Cat C on a specific day, if they were heavy and icing conditions exist. This wouldn't usually affect the which SID to follow, but will certainly affect with approach plate and minimums you have in the likes of a circling approach.

Growler!!! · 21-08-2015 08:04AM

Alaba320 wrote: »

You can have prop aircraft in cat C and jets in cat B. Aircraft categories have nothing to do with what means of propulsion the aircraft has, it is based on speed of the aircraft (clean stall speed X 1.3)

I'm not familiar with the Dash 8, but this could be the reason the don't make the early turns. Also just to add confusion...a turboprop which usually lies in Cat B, could end up in Cat C on a specific day, if they were heavy and icing conditions exist. This wouldn't usually affect the which SID to follow, but will certainly affect with approach plate and minimums you have in the likes of a circling approach.

Thanks for that:D
The question was why do turbo props turn early. The main TP out of Dub is the ATR. Which uses the Cat A/B departures.

BonkeyDonker · 21-08-2015 11:23AM

Out of curiosity is there a list of aircraft that fall into each category at normal operating conditions?

eatmyshorts · 21-08-2015 11:38AM

There's a bit of confusion here. Aircraft Categories A/B/C/D/E are APPROACH categories. They have nothing to do with departure procedures.
They are referenced in order to comply with airspace and obstacle clearance considerations on approach procedures.

www.skybrary.aero/index.php/Approach_Speed_Categorisation

Irish Steve · 21-08-2015 12:29PM

eatmyshorts wrote: »

There's a bit of confusion here. Aircraft Categories A/B/C/D/E are APPROACH categories. They have nothing to do with departure procedures.
They are referenced in order to comply with airspace and obstacle clearance considerations on approach procedures.

www.skybrary.aero/index.php/Approach_Speed_Categorisation

See post 5 above, IAA DEPARTURE procedures for CAT A/B aircraft

A thru E are Aircraft PERFORMANCE categories, and the specific details refer to speeds, climb capabilities and other fundamental aspects of the way the aircraft operates, for more specific information, this is an excellent detailed reference site

https://contentzone.eurocontrol.int/aircraftperformance/

Alaba320 · 21-08-2015 08:29PM

eatmyshorts wrote: »

There's a bit of confusion here. Aircraft Categories A/B/C/D/E are APPROACH categories. They have nothing to do with departure procedures.
They are referenced in order to comply with airspace and obstacle clearance considerations on approach procedures.

www.skybrary.aero/index.php/Approach_Speed_Categorisation

There is no confusion here, aircraft categories go for take off as well as approach.

smurfjed · 22-08-2015 12:55AM

There is no confusion here, aircraft categories go for take off as well as approach.[\quote]

Alaba320, that appears to be a CBT screenshot. Can anyone point me towards a regulation showing that the Approach categories are also used for takeoff.

Doors about to close, so I don't have time to google.

eatmyshorts · 22-08-2015 04:32AM

Alaba320 wrote: »

There is no confusion here, aircraft categories go for take off as well as approach.

SIDs at some airports like Dublin may have Category designators. However, that is nothing to do with aircraft categorisation.
Aircraft categories are only in relation to approach procedures.

gctest50 · 22-08-2015 04:39AM

It's to take advantage of the extra lift

Since they are so ugly the ground repels them, it has been found grass and trees repel them slightly more than concrete and tarmac

eatmyshorts · 22-08-2015 04:53AM

gctest50 wrote: »

It's to take advantage of the extra lift

Since they are so ugly the ground repels them, it has been found grass and trees repel them slightly more than concrete and tarmac

Isn't that helicopters?

gctest50 · 22-08-2015 05:01AM

eatmyshorts wrote: »

Isn't that helicopters?

They seem to have scarce reserves of it and run out of it far too often

Teebor15 · 22-08-2015 09:14AM

Aircraft categories are only in relation to approach procedures.

This is incorrect. Although the approach speeds are what defines which category (A,B,C,D,E,H) an aircraft belongs in it does not mean that these categories are only used for approach procedures. They are also used for departure procedures, and holding procedures too while we're at it.

22-08-2015 09:54AM

aircraft approach category
The grouping of aircraft based on speed. The categories are as follows:

(a) Category A-speed up to 90 kt;

(b) Category B-speed of 91 to 120 kt;

(c) Category C-speed of 121 to 140 kt;

(d) Category D-speed of 141 to 165 kt; and

(e) Category E-speed above 165 kts

Aircraft departure speeds are based on the above speeds and categories as well but

Remember that the manoeuvring speed specified here does not relate to Va, but instead relates in this case to the planned speed the pilot will manoeuvre the aircraft during the departure phase of flight.

http://www.skybrary.aero/index.php/Approach_Speed_Categorisation

22-08-2015 09:57AM

Teebor15 wrote: »

This is incorrect. Although the approach speeds are what defines which category (A,B,C,D,E,H) an aircraft belongs in it does not mean that these categories are only used for approach procedures. They are also used for departure procedures, and holding procedures too while we're at it.

There's no group H by the way

Teebor15 · 22-08-2015 10:05AM

There's no group H by the way

There is actually. Category H is for Helicopters.

Teebor15 · 22-08-2015 10:13AM

Aircraft departure speeds are based on the above speeds and categories as well but

Quote:
Remember that the manoeuvring speed specified here does not relate to Va, but instead relates in this case to the planned speed the pilot will manoeuvre the aircraft during the departure phase of flight.
http://www.skybrary.aero/index.php/A...Categorisation

Just to add another piece of useless information, the maximum turn speeds for the different Categories of aircraft for departure procedures are based on the missed approach speed + 10% (To allow for the extra weight a departing aircraft would have versus an arriving aircraft executing a missed approach.)

Growler!!! · 22-08-2015 10:44AM

Deleted User wrote: »

aircraft approach category
The grouping of aircraft based on speed. The categories are as follows:

(a) Category A-speed up to 90 kt;

(b) Category B-speed of 91 to 120 kt;

(c) Category C-speed of 121 to 140 kt;

(d) Category D-speed of 141 to 165 kt; and

(e) Category E-speed above 165 kts

Aircraft departure speeds are based on the above speeds and categories as well but

http://www.skybrary.aero/index.php/Approach_Speed_Categorisation

So an ATR 72 climbing at 170kts is in Category E? Why is it turning at 750ft out of Dublin which is a category A/B departure. Unless it relates to the approach speed!

Teebor15 wrote: »

There is actually. Category H is for Helicopters.

There's a performance category A for helis. It involves a twin or larger climbing in reverse from a platform or structure, having sufficient height and speed to land back in its take off spot in the event of engine failure.

eatmyshorts · 22-08-2015 11:05AM

Can any one show me a reference that states that SID categories are based on Aircraft Approach Categories?
That just doesn't make sense.

eatmyshorts · 22-08-2015 11:07AM

Teebor15 wrote: »

This is incorrect. Although the approach speeds are what defines which category (A,B,C,D,E,H) an aircraft belongs in it does not mean that these categories are only used for approach procedures. They are also used for departure procedures, and holding procedures too while we're at it.

For holding procedures that are part of a published instrument approach procedures.
Not for enroute holding.

Teebor15 · 22-08-2015 11:08AM

So an ATR 72 climbing at 170kts is in Category E? Why is it turning at 750ft out of Dublin which is a category A/B departure. Unless it relates to the approach speed!

No. The criteria for deciding what category an Aircraft belongs in is based on the approach speed. So an ATR 72 is Cat B. When a Cat B aircraft departs it follows the CAT B procedure. Simple. The departure speed has no bearing on what Cat Dep an aircraft follows. But adding to my useless information I posted earlier the max speed for a Cat B aircraft flying a turning departure is 165 IAS.

There's a performance category A for helis. It involves a twin or larger climbing in reverse from a platform or structure, having sufficient height and speed to land back in its take off spot in the event of engine failure.

I don't think that has anything to do with Instrument app/dep procedures which is the tread topic.

As I said earlier Category H is for Helicopters. It would be used where Instrument procedures were required for somewhere like a heliport or in rare cases a helipad at a hospital. They are not published for airports because a Helicopter come under Cat A for airports and thus will use the CAT A chart for the appropriate runway.

Hope this helps.

eatmyshorts · 22-08-2015 11:09AM

Teebor15 wrote: »

Just to add another piece of useless information, the maximum turn speeds for the different Categories of aircraft for departure procedures are based on the missed approach speed + 10% (To allow for the extra weight a departing aircraft would have versus an arriving aircraft executing a missed approach.)

Why would and aircraft executing a missed approach be following an SID procedure?

Teebor15 · 22-08-2015 11:27AM

Why would and aircraft executing a missed approach be following an SID procedure?

Sorry I'm not with you...where did I say that a aircraft executing a missed approach would follow a SID?

Why do prop planes turn away from the runway so soon

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