Turn radius

Cheezypoof

Well-Known Member
I was training a developmental and we came across a route that was a 90 degree turn. The jet was at Flight Level 3-0-0 coming from the north flying a 180ish heading. At the fix ASHEN his next point was GSH which would be a 90 degree turn to the west. Obviously a jet flying 500 knots isn't going to make a 90 degree turn on the dime I told him... but he seemed to think because he cut it short it was a possible pilot deviation.

So we tried looking it up and couldn't find anything of reference in the 7110.65, AIM, or FAR 91.. quick searching though. I know with RNAV fixes they can be fly by or fly over, but this was direct routing a /G could fly so I didn't think that applied.

So what can I tell him? is there a certain limit you pilots have with turns like this?
 

MoMatt

Well-Known Member
I'd suspect your definitive answer is in TERP's. Someone with more recent instrument training may chime in with a better answer, but here's my understanding:

There are only certain waypoints that are designated as "fly-over", and they include final approach fixes, initial approach fixes, holding fixes and any other waypoint specifically designated on a chart as fly-over. This is to ensure obstacle clearance.

Everything else not specified above is a "fly-by" waypoint and does not need to be flown over. Imagine, especially with your 500 knot jet, if it had to fly over every single waypoint, it would take 50 miles to get back on course every time it passed a waypoint. By leading the turn, the plane never deviates from the course centerline, making it more efficient and much more comfortable for the passengers.

Regarding certain limits on turns over waypoints, and assuming we're now talking only about fly-over waypoints, any limits we have are in regard to speed. If we stay below a certain speed (category A, B, C, D, E...) and make our turns at standard rate (or 25 degrees of bank), and stay on course, we won't hit anything. That's how approaches are designed via TERPs.

Hope this helps!
 

Boris Badenov

He comes to save the day in a broken truck.
If he's at FL300, I can't see how it's a Terminal procdure. You could aim for Everest at that altitude and still miss by rather a lot.
 

greg1016

Trustworthy Source
We had a crew briefing a few months or maybe a year ago regarding a deal that occurred at another center because an Airbus turned earlier than expected at a fly-by way-point because its FMS would not bank the aircraft more that 20 degrees or something like that, and to execute the turn and stay within the bank limit, the autopilot turned the aircraft waaaaayyy early.
 

Vector4Food

This job would be easier without all the airplanes
We had a crew briefing a few months or maybe a year ago regarding a deal that occurred at another center because an Airbus turned earlier than expected at a fly-by way-point because its FMS would not bank the aircraft more that 20 degrees or something like that, and to execute the turn and stay within the bank limit, the autopilot turned the aircraft waaaaayyy early.
Seen this quite a bit with Falcons for some reason
 

C150J

Well-Known Member
FYI, most Collins FMSs will command a up to 12NM prior to a fix if it's not a fly-over waypoint.
 

Crockrocket94

Well-Known Member
Ive seen Universal FMS's start turns very early in the terminal/approach mode but usually not by more than 5nm up high.
 

Bernoulli Fan

Controller
We had a crew briefing a few months or maybe a year ago regarding a deal that occurred at another center because an Airbus turned earlier than expected at a fly-by way-point because its FMS would not bank the aircraft more that 20 degrees or something like that, and to execute the turn and stay within the bank limit, the autopilot turned the aircraft waaaaayyy early.
We just got a read and initial on HAL replacing their oceanic fleet with A330s. There is a turn they make around military airspace before heading out across the Pacific that the Airbus won't make without hitting because of the 20-degree bank limitation. As I understand it, there is nothing the pilot can do to increase the angle of bank, either. Thanks, Airbus.
 

Autothrust Blue

"Duuuuuude."
We just got a read and initial on HAL replacing their oceanic fleet with A330s. There is a turn they make around military airspace before heading out across the Pacific that the Airbus won't make without hitting because of the 20-degree bank limitation. As I understand it, there is nothing the pilot can do to increase the angle of bank, either. Thanks, Airbus.
Well, there probably IS something the pilots can do about it, because that airplane can be made to turn steeper than that in manual flight...
 

Vector4Food

This job would be easier without all the airplanes
Well, there probably IS something the pilots can do about it, because that airplane can be made to turn steeper than that in manual flight...
Agree 100%, even the Scarebus can be flown manually.

Solution to this problem? Write up every single aircraft that violates airspace because of a "bank limitation"
 

Bernoulli Fan

Controller
Agree 100%, even the Scarebus can be flown manually.

Solution to this problem? Write up every single aircraft that violates airspace because of a "bank limitation"
Well, the AWE pilot who came and briefed us on Airbus flying said pilots couldn't do it. Maybe he meant the company doesn't want them to do what would be necessary to increase the bank angle. Would that require alternate law or something?

What would the violation be? I was looking through the CFRs and the AIM, thinking it said standard rate turns must be made under IFR somewhere in there, but I couldn't find it.
 

BWER

Well-Known Member
We had a crew briefing a few months or maybe a year ago regarding a deal that occurred at another center because an Airbus turned earlier than expected at a fly-by way-point because its FMS would not bank the aircraft more that 20 degrees or something like that, and to execute the turn and stay within the bank limit, the autopilot turned the aircraft waaaaayyy early.
If you are using minimum seperation where a course change is coming up, you should be using present heading. To me that is an oversight on the controller not realizing the aircraft had a turn coming up. I was trained to anticapate aircraft making turns prior to the fix. Honestly I was trained to put any aircraft on headings that were going to be close, a throwback to the /W days.

Most times course changes are small 10-30 degrees, so its not a big deal when they make the turn. On big turns though it is very noticable. I would say a good bit of controllers fall under that catagory of "who cares of what the FAR/AIM says." I simply keep planes 1000 feet or 5 miles apart. Me personally here, if I dont think a plane making a turn is going to start it early, well I deserve any and all credit for a deal because of it.
 

greg1016

Trustworthy Source
IIRC this Airbus we were briefed on was on a SID and the turn he was making was 70-80 degrees. The controller was anticipating a turn, it just started about 5nm earlier than expected.

Bernoulli Fan

I went to that briefing too, and I remember a lot of questions being asked to the pilot about hand flying the aircraft. I was under the impression it could be hand flown to the same tolerances as a boeing.
 

Bernoulli Fan

Controller
I went to that briefing too, and I remember a lot of questions being asked to the pilot about hand flying the aircraft. I was under the impression it could be hand flown to the same tolerances as a boeing.
You New Yorkers must be of a more curious type. We all just listened to the briefing, clapped at the end, and said to ourselves, "Ooh, a pilot!"
 

greg1016

Trustworthy Source
You New Yorkers must be of a more curious type. We all just listened to the briefing, clapped at the end, and said to ourselves, "Ooh, a pilot!"
Well, the controllers here are concerned that too much cockpit automation is resulting in under-skilled pilots. Our domestic areas don't exactly have wide open airspace, they run them tight.
 
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