GA aircraft - startup before clearance

[Claudiu Dragomir]

Most GA aircraft seem to have a short battery life (2 minutes or so).

Some airports require approval before startup.

How do you manage that? Do controllers know that I can’t copy clearance before startup? (my radios will cut out mid sentence).

[Raul Ferraz]

very often you call the controller and on that initial call you only request start-up.
Later, after engine is fired up and everything powered up on your aircraft, you ask for the clearance

[Robert Shearman Jr]

Real-world, there's also the possibility to be connected to groundpower, or, to have obtained your clearance by phone from inside the building before heading out to the plane.

On VATSIM, it's not common that controllers can actually see whether you've started the plane or not -- so if you're not moving, you're probably not hurting anything.

[Charan Kumar]

All my GA flying (r/w USA) I only call up after engine start, even if I have a handheld radio. I follow the same online. Granted, I will be on the ramp, on non movement area before starting. You should be able to do the same. As stated before, do not move and you should be good. 

[Andreas Fuchs]

Depending on the country and airport, you will only receive your departure instructions when talking to a tower controller. And often you will start your engine without clearance and only call in afterwards. If they then tell you to expect x minutes delay, you can shut down again.

[Joshua Jenkins]

The startup clearance is also more important for larger aircraft as their jet blast (or prop wash) can extend far behind the aircraft onto, say a taxiway where a poor C152 might be crossing. This effect can be further magnified if the larger aircraft is doing a cross-bleed start where it often involves spooling up the running engine a significant amount to get the bleed air pressure necessary to start the opposite engine.

The prop wash from something small starting up (like a C172) is unlikely to cause much danger/damage to other aircraft or secured objects behind the aircraft.

[Martin Loxbo]

10 hours ago, Claudiu Dragomir said:

How do you manage that? Do controllers know that I can’t copy clearance before startup? (my radios will cut out mid sentence).

It's a good question, and something that used to bug me back in the day when I would fly something that really should have an APU/GPU but which wasn't simulated so the battery would die after a few minutes. To start with (no pun intended), that 2 minute battery life is probably not very realistic. On the other hand waiting for a clearance could be a lot longer than 2 minutes in many cases.

While it may seem obvious that startup approval is all about starting engines, in Europe this approval is more connected to flight plan expiry and slot times. In real life, European ATC (there may be some states with more relaxed rules) will only approve startup within +/- 15 minutes of your EOBT (Estimated Off-Block Time) for an IFR flight. If you call too early, you'll either have to wait or send a flight plan with an earlier EOBT, and if you call too late you'll have to send a "delay message" to update your EOBT to a later time.

The time window to call for startup gets even smaller at airports with A-CDM procedures, which is most major airports in Europe these days. The exact procedures can vary from airport to airport, but in general at these airports every flights needs a TOBT (Target Off-Block Time). The TOBT is updated by the handling agent to make sure it's realistic and actually reflects the time a flight is ready to depart (here "ready" means doors closed, ground equipment removed and ready for engine start or pushback as required). Based on the TOBT, ATC will assign a TSAT (Target Startup Approval Time) that takes into account if the flight has a slot time (i.e. a CTOT - Calculated Takeoff Time), taxi times to the departure runway, traffic conditions at the airport etc. Normally at these airports you have to call within +/- 5 minutes of the TSAT in ordered to hear that awaited "startup approved". If you call at TSAT +6, expect to hear "your TSAT has expired", and you now have to arrange a new TOBT with the handling agent since apparently you were not "ready" at the TOBT which you promised you would be... 

So where am I going with this? Well, as you can see there's more to the ATC phrase "startup" than actual engine start - it's more of a way of managing the traffic flow. There can also be situations where you need to start the engine(s) where you do not have the "flight plan related" startup approval. For example, if you have a slot (CTOT) that means you'll have to wait for a while on the ground, you may need to leave the gate/parking stand clear for other traffic. In some cases there's no need to start an engine as you can simply get pushed back and towed away, but in other cases you may need to start the engines, taxi to some other location and shut the engines down. There could also be technical reasons such as yours (battery dies in 2 minutes), or something that's happened to me in the 737: APU is inoperative, it's 30°C outside, you have a plane full of passengers and there is no external air conditioning available. This means the only way to cool the cabin is to start an engine in order to be able to run the packs, but if you ask ATC for "startup" they will deny it unless you call within the correct EOBT/TOBT/TSAT windows. In this type of situation you need to explain in more or less clear language what you need to do and why, such as "request to start one engine on stand (for technical reasons / for air conditioning)". Then the controller should understand that your request has nothing to do with a flight plan or IFR clearance, and they should allow it, if it's safe to do so (they may need to send someone to check that the area is clear regarding jet blast etc as Josh mentioned).

[Andreas Fuchs]

8 hours ago, Martin Loxbo said:

To start with (no pun intended), that 2 minute battery life is probably not very realistic.

Absolutely. If this happened in a real aircraft, it would be a no-go decision, because a battery should last at least 15 to 20 minutes, if not longer (on reduced load = partial avionics active). Depending on the SIM you use, in FSUIPC there is an option where you can extend battery life to infinite.

[Tobias Dammers]

Also note that at many European airports, the GA apron is uncontrolled, which means that you can start your engine, pushback, and taxi on the apron, at your own discretion (but you are also responsible for making sure you're not causing any problems by doing so). So you'd start your engines as needed, call Delivery for your IFR clearance, and then just pushback and taxi as needed, and call up Ground (or Tower, as the case may be) when you reach the limit of the uncontrolled apron (usually a designated apron exit point).

[Claudiu Dragomir]

Thank you very much for the detailed answers. It starts to make sense how all this fits with real-life constraints.