There are many steps involved with getting a commercial airliner into the air. As such, procedures have been implemented over the years to do this as safely as possible. One critical step in this process is to ensure that an aircraft is permitted by air traffic control to actually do the taking off from any given runway*. This is crucial since hurtling a jet full of fuel down a runway that has another jet full of fuel landing/crossing said runway makes a large and expensive mess. To stop this happening, clearance from ATC to take off is part of the take off checklist, which contains all the necessary steps. Except it doesn't always work.

Recently, I'll link it when I find it again, there was an incident where a regional jet was cleared to hold (not take off) and started the take off roll anyway. As they crested a rise in the runway the vertical stabilizer of a Boeing 777 came into view. Erring on the side of caution/employment, the crew aborted the take off. Seconds after, they then received clearance, the 777 was essentially finished crossing by this point.

The problems here were some expectation bias, but also because the process of getting clearance is essentially verbal via the radio, and passing that point on the checklist relies entirely on one/both crew remembering if they heard that clearance. This is where the expectation bias can creep in. If you do the same trip 100x, and you hear clearance to hold at the end of the runway then almost immediately clearance to take off, you may think you heard the second part just because 100x before, you did.

The problem being, there's no visual reference like you get with nearly every other checklist item. Other items, such as the strobe light that should be on before take off, you can check by looking at the switch. So why not make clearance the same?

In this way, while making the radio call to obtain take off clearance, your finger can be on the switch... as you hear it, you flick the switch. Both pilots now have visual reference as to whether this has happened. But, we can do more than this. If this switch were linked into the avionics, in the "no" position, several safety interlocks might be added, for example, engine thrust might be limited to 30%** to prevent un-cleared take off rolls.

Even better, a light as visual reference would be useful for all in range. The best situation would be for the aircraft to transmit the status to ATC to highlight any disagree status with the controller.

*A runway is preferable. It's considered poor form to be landing on a taxi way, Harrison. ** Or whatever max reasonable taxi thrust might be for the type, for a Cessna 172 in mud, that might be 127%.
-- bs0u0155, Jan 26 2021

//that phrase "take-off" is a problem.//

I agree, the natural progression is to remove from the cockpit anyone named "Charlie" or "Juliet" to remove the possibility of confusion. However, my friend Fueldump Geardown disagrees strongly.
-- bs0u0155, Jan 27 2021


[bs0u0155]; along with Mike, Oscar, anyone who is a father (Papa) & Romeo?
-- neutrinos_shadow, Jan 27 2021


// Mike, Oscar, anyone who is a father (Papa) & Romeo?//

Yep. Gone. Safety you see, can't argue with safety. Trust me I've tried.
-- bs0u0155, Jan 27 2021


Take off already eh... hosers.
-- 2 fries shy of a happy meal, Jan 27 2021


//Take Off Clearance Switch//

OK, I've done that. What should I do with this dangling wire?
-- pertinax, Jan 27 2021


Based on your logic, it seems very strange that we allow pilots, who vary hugely in experience, intelligence, risk-appetite, sleep-deprivation, etc. to fly aeroplanes at all in the busy, complex environment of an airport. Surely it would be far better to have aeroplanes flown by remote control from the air traffic control tower until they’re a few miles away from the airport?
-- hippo, Jan 27 2021


Even better would be to divert the aeroplanes away from the airport and get them to land and take off somewhere else, somewhere quieter with fewer other distractions around.
-- pocmloc, Jan 27 2021


You had me until you linked it to the avionics. That would add a number of points of failure. What happens when the computer decides you didn't actually have clearance and cuts your power halfway through the takeoff roll?
-- Voice, Jan 27 2021


What's needed is a system equivalent to the metal keys, used on the railways to ensure that trains could not enter shared lines, as the key was needed to open the points, and there was only one key. This made it impossible for two trains to have it at once.
-- xenzag, Jan 27 2021


<marketing department>//a number of points of failure// - this is just another way of saying "points of success". </marketing department>
-- hippo, Jan 27 2021


// What's needed is a system equivalent to the metal keys, used on the railways to ensure that trains could not enter shared lines, as the key was needed to open the points, and there was only one key. This made it impossible for two trains to have it at once.//

This is actually possible. Put a light in the cockpit and pass a cryptographically signed (and timestamped) key the hardware uses to turn on the light. No light, no permission. It can use a wireless network for the airplanes to pass it about. Contains one button to request the key and one to pass it on. Is automatically passed when the signal timing indicates an airplane has departed.The control tower has the authority to revoke and re-issue when needed.
-- Voice, Jan 27 2021


//...What happens when the computer decides you didn't actually have clearance and cuts your power halfway through the takeoff roll?//

This is just how it should be implemented. I suggested the idea that say ~30% of total thrust be the maximum unless the clearance switch is engaged. If we think what would happen in that scenario, it all ends quite safely I think. Say we have made it to the end of runway, we have run the before take off checklist Pilot Flying (PF) advances thrust levers with the brake engaged.

Now, in a lot of aircraft, the engines are spooled up to 40% N1 and allowed to stabilize before advancing further, to prevent any asymmetry. If we had a clearance switch interlock here, either the thrust levers wouldn't go to 40% or the engines would stabilize at 30% and we'd have a big no-go red flag. Say the clearance switch limited to 50%*, we stabilize just fine at 40% N1 at the end of the runway and then advance to 100%. In this scenario again, either the thrust levers don't go there, or, the aircraft begins barreling down the runway accelerating far too slowly. Pilot Monitoring, while calling out the speeds should notice the lack of acceleration rate, PF, should notice too. Both would definitely notice that the thrust levers are firewalled while the engines level out at 50%. Again, big red flag. Abort take off roll, bring to a stop safely. The big benefit being that the aircraft was never in a high enough energy situation to fly. The worst case scenario is not noticing the take off roll is going on forever and crashing through the lights/antennas off the end of the runway at an even 80 knots, but hopefully some kind of alarm should be going off well before that.

*again, I don't know how much thrust is required for every conceivable taxi situation, I imagine heavy aircraft sitting on hot tarmac might need some significant unsticking on occasion.
-- bs0u0155, Jan 27 2021


It would be safer if aeroplanes took off really slowly
-- hippo, Jan 27 2021



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