White Knight
It is really very simple. Pans Ops covers the all engine profile and the company is legally responsible for the (n-1) profile till 1500 ft.
Basically speaking, there are differences between different airlines, some ops departments cover you till the minimum requirement of 1500 ft and some use a wider area, wind profiles then others and will even cover you until the enroute structure and then you are on you own.
If you deviate from the area and subsequent routing that has been checked by the company then you can do so under an emergency, but you have to have a dammed good reason to do so.
As far as ATC s concerned, they are responsible for separation with other aircraft (depending on the class of airspace, I presume you are in a CTR most of he time) and the pilot in command is responsible for obstacle clearance.
Basically what the performance department will do is to give you a routing straight ahead with an acceleration segment for cleaning up the aircraft. Only if payload is that much affected by obstacles will they give you a routing with a turn.
In my previous airline the chief pilot had obliged the perfo dep (for certain complicated aeroports) to put the (n-1) routing on the SID whatever the cost in payload.
If you decide to clean up the aircraft then you are trading your climb gradient for acceleration towards a speed with less drag.
If the decision was made to return to the field of departure then that is not necessarily the thing you want to do. You may then elect to climb instead to a minimum of (MSA -700) as this altitude will cover you with the minimum obstacle clearance.
The only other option you have for an early turn is to use the protected area for circling approaches and the circling MDA.
If you are sure you can meet the required climb gradient of the SID you may elect to stay on the SID because that is where ATC will expect you to be and they organise their flow management around that principle.
1% climb gradient is about 60ft/Nm so 2,4 % is about 150 ft / Nm and you will need 10Nm till 1500ft and a bit more than 20 Nm for 3000 ft since you will not be able to maintain the 2.4 % due to engine performance and the fact that you accelerate in TAS with IAS constant.
It is of course your right to call a mayday and throw you aircraft in the hands of ATC and have them remove all other traffic. But, ATC are human beings just saying you are responsible to get the others out of he way is not the same as achieving that.
On a busy airport a simple go around under normal conditions already starts some kind of domino effect upon the other traffic with all consequences indeed.
Depending on the nature of the failure you will need considerable time to get ready for the approach probably with some dumping in an area that has been designed for that.
So I can very well imagine that ATC has some preferences as to confine the aircraft to a designated holding area to reduce the knock on effect on other traffic and take it from here.
As a pilot I also prefer to get in a hold thereby reducing the crew load and he effect of the split cockpit.
So if ATC requests you to go to the hold and you can comply with that request in a safe manner then that’s the best thing to do.
In order to get to the MHA and achieve that objective quickly you may elect to delay the acceleration or not accelerate at all.
Definitely will you not accelerate until all turns are completed since that achieves nothing good if you are in a (n-1) configuration.
Early turns in VMC at an airport you know are acceptable but what did you really achieve with that except anything else than a complete surprise to ATC who may well argue that under those circumstances can not reasonably be expected to continue to cater for separation.
Finally, since most operations are carried out from home base I think it’s a good idea that management talks to ATC and work out a plan beforehand.
Edited for clarity:
With climb to (MSA -700) I mean climb straight ahead till (MSA -700) before you want to make any turn if you have elected to deviate from he standard profile.