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JLP731

Autobrakes RTO?

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Hello all-

 

Quick question! I like to be slightly different sometimes, and often try to put various different airframes through their paces.

This will involve things like stall tests, various failures, all sorts of weird and wonderful maneuvers.

My favourite though, is testing our Rejected Take-offs in different situations, weather, states of decay on the aircraft, etc.

 

I don't notice a huge deceleration on Autobrakes RTO in this aircraft. I am aware the default FSX brakes message is suppressed and you use a custom ground friction model.

I would expect brand new brakes, with no failures or any other settings altered, to really throw me forward in my seat and stop the aircraft fairly quickly.

 

I've tested this with and without reverse thrust, with some difference detected.

 

Are RTO brakes not supposed to be the same as MAX autobrakes? Should it not be a lot more effective bringing the aircraft to a halt on the runway?

 

Manual braking is FAR more effective than RTO. Maybe I'm missing something, or I'm stupid? Maybe RTO autobrakes aren't supposed to be as effective as I expect them to be?

 

I would guess in a real-world RTO, they are probably only active for a few seconds until the PF would take over manual braking.

 

Thoughts and insights would be most welcome!

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20 minutes ago, JLP731 said:

Are RTO brakes not supposed to be the same as MAX autobrakes? Should it not be a lot more effective bringing the aircraft to a halt on the runway?

Hardware brakes? If so, ensure they're properly configured. They might actually be tripping the autobrakes off.

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Kyle Rodgers

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Hi,

Do you initiate the rejected takeoff above 85kts ground speed? Because RTO will not trigger activate the brakes below that speed.


Romain Roux

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10 hours ago, JLP731 said:

Are RTO brakes not supposed to be the same as MAX autobrakes?

You should treat RTO Autobrake as your thinking about stopping time!  As Romain has already said, It will only activate during the takeoff roll (assuming it has been pre-selected first!) when the airspeed is above 85kts AND all four thrust levers must be closed.  Maximum brake pressure will then be applied to the main wheels with antiskid protection, so I also agree with Kyle about your configuration, because you shouldn't notice any difference in the deceleration rate when you apply maximum manual braking. The stopping distance will of course depend primarily on the gross weight of the aircraft, as well as the runway conditions, etc.

Assuming you are the Captain, the correct technique for a rejected takeoff above 85 kts is to close all four thrust levers simultaneously applying maximum manual braking.and then immediately deploying the speedbrakes.  All four thrust reverse levers are selected up to the interlock and if above 100kts full reverse is used on the available symmetrical pair/s of engines until a safe stop is assured.  Idle reverse is normally sufficient for a RTO below 100kts

Bertie Goddard 

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Hi all,

Thanks for your replies. I'm out at work today and I'll check again tonight, maybe my hardware brakes are conflicting, I shall have a look at FSUIPC and see if I get any luck.

I don't recall the speeds but I shall keep that in mind, as I said I'm sure you really only rely on the auto brakes for a few seconds while you coordinate everything else and then by instinct you'd manually brake anyway! 

 

Really aooreciate your thoughts, chaps.

 

Josh Park

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 Bertie,

Your RTO technique is not standard. At RTO, close all P/L’s and select all reversers to interlock. Brakes will go to Max braking (as selected!) and spoilers will deploy on reverse selection. Don’t use Manual braking! That is the whole idea of the RTO Autobrakes. 

Use reverse thrust until speed is 60 kts.

Disarm autobrakes at save speed by manual brake input.


René Moelaert

PMDG 744 Tech Team

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5 hours ago, fleng200 said:

 Bertie,

Your RTO technique is not standard...............Don’t use Manual braking! That is the whole idea of the RTO Autobrakes. 

René,

Sorry to say, not where I come from it isn't!  But then I suppose it all depends on which operator you fly for, doesn't it? 

Rejecting close to V1`on a limiting runway is probably the most critical scenario for a max weight B744 takeoff, which is why the decision to stop must never be taken lightly.  In fact in most cases it may be safer to continue, which is why the decision is often left up to the Captain above 80 kts and even then you should normally only reject for a major malfunction such as a fire or an engine failure (2 or more parameters). 

The thinking behind an SOP not to rely on the RTO Autobrake to stop the aircraft is down to the fact that if the RTO Autobrake doesn't kick in as expected for any reason when rejecting close to V1 then by the time one of the pilots recognises the fact and remembers to apply and maintain maximum manual braking there is a very good chance the aircraft will not stop before the end of the runway - and neither pilot will collect their pension!   The flight crew's actions when carrying out a RTO need to be well-trained, rehearsed and almost instinctive, which is why RTO's are regularly practised in the simulator and why each pilot's RTO actions should always be discussed (using touch drills) during the pre-flight briefing prior to every flight.

Incidentally, this same SOP philosophy applies to the use of the Speedbrake Lever during a RTO, because the ground spoilers have been known not to deploy automatically on rare occasions.  During every RTO the Captain is required to deploy them manually, even if the co-pilot is the handling pilot at the time.  As you say, they will usually deploy automatically, but it is essential to ensure that they do so in order to gain maximum deceleration force from the aerodynamic drag at the higher speeds, together with the full weight of the aircraft bearing down on the wheels, tyres and brakes.

I remember my very first flying instructor saying to me that there are as many ways of flying an aircraft as there are pilots, so I'm sure you and I could enjoy debating the merits of our differing procedures and SOP's for years. Maybe we can agree to disagree on the best RTO SOP?  However, I know which of our two RTO handling procedures I prefer using and recommend on the grounds of its enhanced flight safety.

Regards, Bertie           

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The QRH Man.1.3 allows for either autobrake or manual braking during RTO.  No need to debate this as it certainly is an operations policy item.  It also calls for raising the speedbrake lever and maximum braking until stopping on runway is assured. The interesting question is do you stop on the runway or roll clear before stopping because you are going to be in position for some time while responders put out the tire fires and declare a safe condition.


Dan Downs KCRP

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11 hours ago, downscc said:

The interesting question is do you stop on the runway or roll clear before stopping because you are going to be in position for some time while responders put out the tire fires and declare a safe condition.

The matter is to stop safely. It is not your problem if you block the runway because you have an emergency. It becomes the job of the ATC to have the aircraft land on another runway or somewhere else.


Guillaume

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11 hours ago, downscc said:

The interesting question is do you stop on the runway or roll clear before stopping because you are going to be in position for some time while responders put out the tire fires and declare a safe condition.

I'm with Guillaume -- stop (turning the aircraft to position any failed engine downwind if appropriate) and deal with it there. Of course, if you have stopped at low speed for a relatively benign issue then you may well be able to taxi off again for another go (or whatever), but personally my view would be that one should always stop fully, set the parking brake and then take a moment to figure out why you have stopped and deal with any immediate actions. Only once absolutely certain it is safe would I move off again.

Part of the issue with the Manchester disaster in 1985 was that the Captain elected to taxi off the runway, thus (amongst other things) delaying the evacuation (and placing the fuselage upwind of the fire).

Interested to hear from others though!

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The FAA certification requires that the aircraft be safe for 5 min after coming to a stop following an RTO, this is part of the test to allow for responder travel time.  An example of what I had in mind is the frequent B77L Delta flight from KATL to KLAX, this bird is very light at takeoff on what is basically a repositioning flight.  Do you close 27R during peak morning traffic or taxi off?  This is certainly a valid question and I would be the last to question the decision of the PIC, I only point out that this is a consideration at the time.  Sure, at times it is a no brainer and you are not moving until 'safed.'


Dan Downs KCRP

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I agree with Guillaume and Simon about staying on the runway; especially if you are flying a large aircraft and have to reject the take off because of an engine fire. In addition, you should also turn the aircraft sufficiently so that the engine on fire is downwind of the fuselage as much as possible (this is standard procedure on the B744 and presumably other large aircraft).

As Simon has said, these two important lessons were learnt following the investigation into the Manchester accident.  Unfortunately, moving the aircraft onto the taxiway also meant that some of the fire appliances had be go onto the grass to get around the aircraft and this obviously made tackling the fire more difficult because of the soft ground. This accident was caused by a fatigue crack in one of the combustion chambers and the Captain and co-pilot handled the emergency and RTO correctly at that time. Hindsight is a wonderful thing in the aviation industry and it is all to easy to lay the blame at the flight crew's feet.  Flight safety is all about learning from accidents like this one.  I believe the Captain in question continued flying with the same airline and eventually went on to become a well-respected Flight Training Manager.

Dan, I take your point about differing operations policies because some are definitely better than others.  However, I would like to pose one last question on the best use of RTO Autobrake if I may. Think about what you might say as the Captain if you are hauled in front of a foreign court and before you are sent to jail for causing a runway overrun accident you are asked by the prosecutor "Why didn't you immediately recognise the aircraft's RTO Autobrake had failed; and when you eventually did and applied maximum manual braking it was much too late to stop on the runway, wasn't it?  You reply that the accident wasn't really your fault, it was down to the failure of the RTO Autobrake - or was it?   The prosecutor says "I rest my case, m'Lud" and off you go clapped in irons for a very long holiday. It's not a very nice position to be in, is it?  But it happened to a crew many years ago after their unfortunate aircraft accident in Greece.

Bertie   

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