kalvado
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Reverse Thrust Activation Question

Fri Jan 25, 2013 11:55 am

Reverse thrust activation logic is being blamed as one of contributing factors to Tu-204 crash in VKO: crew tried to use maximum reverse thrust - but the doors never opened, and engine spooled up as if everything worked normally. Plane ended up with forward thrust close to maximum.
So my question is - what would happen on other types (A or B, or any other jet), if reverse setting above idle is selected, but reversers are not actually deployed? Would engines still spool up, or there is some sort of interlock to prevent that?
People quote A310 in IRK and Lear 60 accidents, but those examples are not very conclusive from my perspective.
 
tdscanuck
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RE: Reverse Thrust Activation Question

Fri Jan 25, 2013 5:56 pm

Quoting kalvado (Thread starter):
So my question is - what would happen on other types (A or B, or any other jet), if reverse setting above idle is selected, but reversers are not actually deployed? Would engines still spool up, or there is some sort of interlock to prevent that?

I'm not sure about Airbus, but a Boeing aircraft has an interlock on the reverse thrust lever. You can't throttle the engine up in reverse until the reversers actually deploy. It's not physically possible (without at least two other independant failures).

Tom.
 
Pihero
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RE: Reverse Thrust Activation Question

Fri Jan 25, 2013 8:23 pm

The system is a bit different on the 320 family : there is no reverse lever, but a reverse range in the throttle quadrant ; the bT/R will deploy on a ground sensing logic and a TLA -thrust lever angle - position in the reverse range provided to thje FADEC.
On the 330... Airbus is back to the dedicated lever for thrust reversing. There is no mechanical lock, just a requirement for the T/L to be at idle. before idle reverse can be selected.
The engine will not spool up until the system is satisfied that reverser doors are out, but still, max reverse thrust will be only available with doors fully open ; ( Simplistic view of a system that's a lot more complex ).
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glen
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RE: Reverse Thrust Activation Question

Fri Jan 25, 2013 8:46 pm

Quoting Pihero (Reply 2):
there is no reverse lever, but a reverse range in the throttle quadrant

Just to make it clear for those not familiar with the system: The A320 has indeed no "classic" reverse levers, which are used to set and modulate the reverse thrust. However there are still reverse levers, which have to be lifted in order to be able to set the thrust levers into the aft range (i.e. reverse range) of the quadrant. In order to modulate the amount of reverse thrust, the thrust levers are then used again. (The more you pull back the thrust lever within the reverse range, the more reverse thrust is commanded)
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Pihero
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RE: Reverse Thrust Activation Question

Sat Jan 26, 2013 12:07 pm

Quoting glen (Reply 3):
there are still reverse levers, which have to be lifted in order to be able to set the thrust levers into the aft range (i.e. reverse range) of the quadrant

Not quite. The selection of the reverse range is achieved , T/Ls at idle, by lifting the two flap-shaped pallets on the forward part of the T/Ls.
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Tristarsteve
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RE: Reverse Thrust Activation Question

Sat Jan 26, 2013 3:27 pm

Quoting kalvado (Thread starter):
if reverse setting above idle is selected, but reversers are not actually deployed? Would engines still spool up, or there is some sort of interlock to prevent that?

To get back to the question, all aircraft I have worked on, starting with the Trident in 1968, have had a throttle interlock system. This prevents reverse thrust beyond idle until the reversers are in position, and prevents fwd thrust until reversers are cancelled and back in fwd position.
On older engines this was a blocking quadrant driven by a cable from the reverser that physically blocked the throttle mechanism. Nowadays it is electrical inside the FADEC.
I would assume that the Tu204 has something similar, but it failed on this occasion.
 
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glen
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RE: Reverse Thrust Activation Question

Sat Jan 26, 2013 3:48 pm

Quoting Pihero (Reply 4):
Quoting glen (Reply 3):
there are still reverse levers, which have to be lifted in order to be able to set the thrust levers into the aft range (i.e. reverse range) of the quadrant

Not quite. The selection of the reverse range is achieved , T/Ls at idle, by lifting the two flap-shaped pallets on the forward part of the T/Ls.

Well, then we are talking about semantics - "flap-shaped pallets" or "reverse levers" - we both talk about the same. The A320 FCOM calls them Reverse levers...
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Pihero
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RE: Reverse Thrust Activation Question

Sat Jan 26, 2013 4:18 pm

Quoting glen (Reply 6):
Well, then we are talking about semantics

Sorry, I nread too fast and thought you meant you had to lift the T/Ls , meaning some sort of mechanical interlock.
Apologies
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flyingturtle
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RE: Reverse Thrust Activation Question

Sat Jan 26, 2013 5:33 pm

Quoting Pihero (Reply 2):
the bT/R will deploy on a ground sensing logic and a TLA -thrust lever angle

Perhaps this is interesting... an accident involving the A320 thrust reverser activation logic: http://en.wikipedia.org/wiki/Lufthansa_Flight_2904


David
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Pihero
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RE: Reverse Thrust Activation Question

Sat Jan 26, 2013 9:47 pm

Quoting flyingturtle (Reply 8):
an accident involving the A320 thrust reverser activation logic:

I studied this accident at length a long time ago and, as usual, it is a matter of a series of unconnected factors suddenly converging to make a normal flight a disaster.
This is , first, the conclusion of the investigation:

}"3.2 Causes of the accident
Cause of the accident were incorrect decisions and actions of the flight crew taken in situation when the information about windshear at the approach to the runway was received. Windshear was produced by the front just passing the aerodrome; the front was accompanied by intensive variation of wind parameters as well as by heavy rain on the aerodrome itself.

Actions of the flight crew were also affected by design features of the aircraft which limited the feasibility of applying available braking systems as well as by insufficient information in the aircraft operations manual (AOM) relating to the increase of the landing distance. "


So : The touch-down, on only one main gear, was long - 770m from the threshold at a ground speed some 40 kt in excess of the reference speed.
There seems to be, from the crew, a rather astonishing lack of understanding of landing prerformance degradation 1/ for slippery runways and 2/ for increased touch-down speeds. The wet runway with patches of water present wasn't considered either. Those calculations are at least available in the aircraft QRH.
To cut a story short, the reverser system - which also participates in the ground spoiler deployment - used to be dependent on both main gear struts to be compressed to allow the reversers and the ground spoilers to deploy.
These conditions were not met and neither the reversers or the speedbrakes were deployed until the 1525 m point (runway is 2800 m long) .

It is interesting to know that the investigators made some recommendations to Airbus :

"4.2 For A320 aircraft manufacturer
4.2.1 Possibility should be analysed to introduce the emergency use of ground spoilers
and thrust reversers independently of meeting the criteria imposed by aircraft logics.
4.2.2 The possibility should be considered to modify the thrust reverser system to enable
use of more than 71% N1 in the emergency.
"

4.2.1 refers to an emergency manual override of both thrust reversing and ground spoilers deployment. That was resisted by the manufacurer who modified the logic :One compressed oleo will get the reversers to idle and cause a partial extension of the spoilers, which would force the remaining gear to make contact with the ground... With both struts compressed, we're backi nto the original specs.
4.2.2 was complied to : the Max reverse thrust has been upped to 80% N1.

The wiki article is in error : the 72 kt wheel spin-off condition is only required in a rejected takeoff situation (don't trust wiki on technical matters )
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ecbomberman
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RE: Reverse Thrust Activation Question

Fri Feb 08, 2013 1:02 pm

Quoting glen (Reply 3):
Quoting glen (Reply 3):
However there are still reverse levers, which have to be lifted in order to be able to set the thrust levers into the aft range (i.e. reverse range) of the quadrant. In order to modulate the amount of reverse thrust, the thrust levers are then used again. (The more you pull back the thrust lever within the reverse range, the more reverse thrust is commanded)

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I presume the amount of reverse thrust 'given' is dictated by how far back you pull the thrust levers back the yellow hash area. That is of course you have to lift the small 'tabs' in front of the thrust levers in order to get to the yellow hash area.

And for the later "buses" it's the matter of pulling back the thrust reverse levers (which is located in front of the thrust levers) when the criteria are met for T/R activation. The more you pull back, the more T/R you get.


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Are my deductions correct? Welcome to make any corrections  
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ecbomberman
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RE: Reverse Thrust Activation Question

Fri Feb 08, 2013 1:46 pm

If you allow me to digress....

With total hindsight and no disrespect to the pilots involved:

Quoting Pihero (Reply 9):
Quoting Pihero (Reply 9):
I studied this accident at length a long time ago and, as usual, it is a matter of a series of unconnected factors suddenly converging to make a normal flight a disaster.
This is , first, the conclusion of the investigation:
http://www.rvs.uni-bielefeld.de/publ...omAndRep/Warsaw/warsaw-report.html

1)Would it be prudent for the pilots to do an aborted landing rather than committing to land? I'm an armchair pilot and watch loads of youtube videos on airbus landings, and it seems to me that most airline SOP would require the PNF to announce DECEL to indicate that plane is decelerating. And if the plane is not decelerating as they have expected (took them 15 sec to decel 20kts, and that it took ~1min for the command of the thrust levers to T/R to actual T/R deployment, surely they would have sensed something wrong, wouldn't it?

2) How does hydroplanning feel like? Would the 'feel' be evident?

3) I understand that some company's SOP is to 'commit to land' when T/R and/or spoilers have been deployed. But if there are discrepancies between the thrust lever command and the ECAM, can they still do an abort landing?

4) If question 3 is yes, would the a/c be able to do an aborted landing at those speeds and at the halfway mark?

Quoting Pihero (Reply 9):
Quoting Pihero (Reply 9):
4.2.1 Possibility should be analysed to introduce the emergency use of ground spoilers

5)Would the plane allow manual deployment of spoilers when the parameters are set for landing for an A32x? I.e.: deactivate ground spoilers and command the spoilers to deploy, say 3/4 open? Or are there any protection to prevent manual intervention?

I may not get all the technical terms right but I've tried my best doing so. My intentions are purely for discussion purposes so please don't flame me   
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Pihero
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RE: Reverse Thrust Activation Question

Sat Feb 09, 2013 2:00 am

Quoting ecbomberman (Reply 10):
Are my deductions correct? Welcome to make any corrections  

Yes, you're correct.

Quoting ecbomberman (Reply 11):
Would it be prudent for the pilots to do an aborted landing rather than committing to land?

Yes, up to the moment T/Rs are deployed. After that point, basically you're committed, there are too many risks for an unlocked T/R.

Quoting ecbomberman (Reply 11):
How does hydroplanning feel like? Would the 'feel' be evident?

It feels actually like a re-accfeleration. Otherwise, the feel is for a very slippery -no pun intended- aircraft.

Quoting ecbomberman (Reply 11):
. But if there are discrepancies between the thrust lever command and the ECAM, can they still do an abort landing?

No, for the reason above.

Quoting ecbomberman (Reply 11):
Would the plane allow manual deployment of spoilers

No ; as iI wrote, the logic was changed in order to allow spoiler deployment with only one oleo being compressed, albeit at half deflection, which will aid the remainin g gear to contact the runway, thus triggering a full spoiler deployment , therefore a reverser deployment and the autobrakes.

Quoting ecbomberman (Reply 11):
it seems to me that most airline SOP would require the PNF to announce DECEL

You're correct, but the "decel"callout will only be because of an autobrake selection. If not, there is no "DECEL" blue light on the autobrake switchlight, hence no callout.
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ecbomberman
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RE: Reverse Thrust Activation Question

Sat Feb 09, 2013 4:15 am

Pihero, sorry for more questions.....

Quoting Pihero (Reply 12):
Quoting Pihero (Reply 12):
Quoting ecbomberman (Reply 11):
it seems to me that most airline SOP would require the PNF to announce DECEL

You're correct, but the "decel"callout will only be because of an autobrake selection. If not, there is no "DECEL" blue light on the autobrake switchlight, hence no callout.

As a pilot, would you think that the 'decel' callout even without autobrake selection (by looking at the PFD) would enhance the overall situational awareness?

How would pilots counteract hydroplanning in situations where they are 'committed to land' so to speak as hydroplanning has been the cause of quite a few landing incidents.

Is it harder to 'cancel out' hydroplanning in a Boeing rather than an Airbus?

Many thanks in advance for the answer.  
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Pihero
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RE: Reverse Thrust Activation Question

Sat Feb 16, 2013 12:31 pm

Quoting ecbomberman (Reply 13):
As a pilot, would you think that the 'decel' callout even without autobrake selection (by looking at the PFD) would enhance the overall situational awareness?

Basically, a call-out is either announcing a PFD / ND / ECAM message or an information that could help the handling pilot.
"DECEL" can only be a message pertaining to the autobrake action having reached 80% of the selection.
It cannot be for anything else.
The technique some of us apply is for the copilot to read airspeeds : 130...110... every to or three seconds until I say "Ok, braking is fine..."

Quoting ecbomberman (Reply 13):
How would pilots counteract hydroplanning in situations where they are 'committed to land' so to speak as hydroplanning has been the cause of quite a few landing incidents.

"Aquaplaning" is one of these overly dramatic concepts for the uninitiated. As a matter of fact, it is , except in very extreme situations - in which you shouldn't be in, anyway, had you prepared your landing - a very transient and manageable phenomenon.
During a landing, you are armed with quite a few powerful weapons : directional control through the rudder pedals is very effective. Differential braking / differential use of the Thrust reversers help keep tracking the centerline easy.
Hydroplaning, as far as I know has rarely been the main factor of an overrun.
I talked earlier of pre-landing preparation : A flooded runway or a "poor" braking action transmitted by the tower means "No No I'll wait until conditions improve and get me into the hold, please." I would also have the landing performance checked and re-checked for wet conditions and select the proper auto-brake, these sorts of things allow one to avoid situations where one doesn't want to be.

Quoting ecbomberman (Reply 13):
Is it harder to 'cancel out' hydroplanning in a Boeing rather than an Airbus?

No. aquaplaning affects tyre-to-ground surface contact. Wer have the same weapons as mentioned above.

You could read a rather well written gen on aquaplaning and techniques here

Hope it helps.

Regards
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