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Faro
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Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 7:53 am

If regulation landing distance does not take into account thrust reverse, what about ground spoilers? Can an airliner be dispatched with inoperative ground spoilers if fair weather conditions prevail at destination airfield? Just how efficient are they at retarding ground speed if the brakes do most of the work anyway and impart a significant deceleration just after touchdown? In that respect, ground spoilers are like T/R, they are most efficient at high ground speeds only so that they very rapidly lose retarding power.

Faro
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OPNLguy
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 8:50 am



Quoting Faro (Thread starter):
Can an airliner be dispatched with inoperative ground spoilers if fair weather conditions prevail at destination airfield?

It depends upon the specific aircraft type and what the MMEL/MEL for it might say, but that said, I've never seen the ground spoilers deferrable on any aircraft types that I've ever dispatched.. (727, 737, DC-9)
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PhilSquares
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 9:02 am



Quoting Faro (Thread starter):
Just how efficient are they at retarding ground speed if the brakes do most of the work anyway and impart a significant deceleration just after touchdown? In that respect, ground spoilers are like T/R, they are most efficient at high ground speeds only so that they very rapidly lose retarding power.

The ground spoilers don't quite work as you describe. What they actually do is destroy the wing's ability to produce lift, thus there is more weight on the landing gear and the brakes become more effective.

As OPNLguy wrote, I can't think of any aircraft I've ever flown that allows for the ground spoilers to be deferred.
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Faro
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 9:07 am



Quoting PhilSquares (Reply 2):
The ground spoilers don't quite work as you describe. What they actually do is destroy the wing's ability to produce lift, thus there is more weight on the landing gear and the brakes become more effective.

Presumably, this facility would only be really necessarily on a wet runway. One would imagine that on a long, dry runway this would not matter as much. Would inop ground spoilers be allowed in such favourable conditions?

Faro
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Tristarsteve
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 9:13 am

Remember that the ground spoilers are the same panels that are the flight spoilers, except for the odd one, usualy the most inboard.
The B767/B757, all spoilers must be operative.
The A320 allows one pair of spoilers inop for dispatch.
Usually the auto function is allowable inop, but the spoilers must work.
 
PhilSquares
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 9:40 am



Quoting Faro (Reply 3):
Would inop ground spoilers be allowed in such favourable conditions?

So, what do you do if you have to divert enroute to a wet runway? Again, every aircraft I have flown, while the MMEL might allow for dispatch, the operator had picked a more conservative approach and not allowe dispatch.
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Faro
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 9:44 am



Quoting PhilSquares (Reply 5):
So, what do you do if you have to divert enroute to a wet runway? Again, every aircraft I have flown, while the MMEL might allow for dispatch, the operator had picked a more conservative approach and not allowe dispatch.

Point taken; does this apply to thrust reverse too? Do operators typically require operational T/R despite laxer MMEL prescriptions?

Faro
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PhilSquares
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 10:02 am



Quoting Faro (Reply 6):
Do operators typically require operational T/R despite laxer MMEL prescriptions?

No, since the thrust reversers are not taken into consideration for certification.
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boeing767mech
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 10:33 am



Quoting Faro (Thread starter):
Can an airliner be dispatched with inoperative ground spoilers if fair weather conditions prevail at destination airfield?

Depends on the operator

Quoting TristarSteve (Reply 4):
The B767/B757, all spoilers must be operative.

Depends on the operator, We are allowed to have one set of ground spoilers or on set of flight spoilers deferred on our 757's, up to 2 sets of flight or ground spoilers on the A-300 and the ground spoilers on the MD-80's (a set being l/h and r/h matched panels).

Quoting PhilSquares (Reply 5):
So, what do you do if you have to divert enroute to a wet runway?

Per the MEL's your not to dispatch an airplane with a deferred set of ground spoilers to a field with visible water or snow on the runway.

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PhilSquares
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 1:13 pm



Quoting Boeing767mech (Reply 8):
Quoting PhilSquares (Reply 5):
So, what do you do if you have to divert enroute to a wet runway?

Per the MEL's your not to dispatch an airplane with a deferred set of ground spoilers to a field with visible water or snow on the runway.

That was a rhetorical question! That's why most operators will restrict the relief to none. In addition, when you have other issues such as a wheel brake inop you end up with a bigger can of worms. As I said originally, the MMEL might offer relief, but in reality, most carriers will have a more stringent approach.
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Jetlagged
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 1:20 pm



Quoting PhilSquares (Reply 2):
The ground spoilers don't quite work as you describe. What they actually do is destroy the wing's ability to produce lift, thus there is more weight on the landing gear and the brakes become more effective.

There's a bit more to it than that. As well as adding braking power (up to the limits of available friction) they add considerable drag, so are effective even without wheel brakes. As Faro said, they are more effective at high speed. Aerodynamic forces vary with the square of the airspeed, so at half touchdown speed they exert a quarter of the force.
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Goldenshield
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 2:34 pm

Quoting Boeing767mech (Reply 8):
Per the MEL's your not to dispatch an airplane with a deferred set of ground spoilers to a field with visible water or snow on the runway.

Whoa there. You're confusing two different areas of the flight. Everything with regard to the MEL is accounted for prior to the flight even departing. If an emergency situation arises while enroute, you go wherever you can get to.

[Edited 2009-05-08 07:35:24]
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PhilSquares
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 3:12 pm



Quoting Goldenshield (Reply 11):
If an emergency situation arises while enroute, you go wherever you can get to.

In theory yes, but how do you explain the decision to go into a field with a medical emergency that's wet or contaminated. Now you are ready to leave and you can't because of the lack of MEL relief.

I realize the MEL applies up to the application of power but heading off with disregard to the MEL after you are on your way is just asking for trouble. That's why all of the airlines I have been associated with have a very strict MEL policy.
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 3:19 pm



Quoting TristarSteve (Reply 4):
The B767/B757, all spoilers must be operative.

One Spolier can be inoperative & deffered under MEL provided its pair on the opposite side is made Inop too on the B752.
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donniecs
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 3:21 pm

The Gulfstream GIII, GV and G550 series aircraft can be dispatched with "automatic ground spoilers system" inop, provided the aircraft is operated IAW the AFM limitations, MMEL 27-3 (cat C). Anti-skip must be operative, flaps 20 used for takeoff, no anti-ice and the expected huge hit in runway length required. Don't forget that you not only take a huge hit not only on landing performance but also with takeoff performance in the event of an RTO.

Quoting PhilSquares (Reply 7):
thrust reversers are not taken into consideration for certification

While not part of certification, Gulfstream includes an interesting chart in the AFM and QRH for landing distances with only reverse thrust (numbers are surprisingly good). As said before a lot of operators have more stringent MMEL policy on ground spoilers.
Charlie - Gulfstream flight mechanic
 
Goldenshield
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 3:24 pm



Quoting PhilSquares (Reply 12):
In theory yes, but how do you explain the decision to go into a field with a medical emergency that's wet or contaminated. Now you are ready to leave and you can't because of the lack of MEL relief.

I meant a true emergency there.  Smile A medical emergency is a matter of time as well, but in regards to this topic, it's not something I would put my crews into a bind with when I know that I have to get that flight back on schedule.
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fr8mech
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 4:30 pm

Ground spoilers can not be deferred, except as individual panels, with their mate as described in the various MEL's. The auto-deployment of the ground spoilers can usually be deferred dependant on the restrictions, usually weather, imposed by the MEL.
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PhilSquares
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 4:45 pm



Quoting Goldenshield (Reply 15):
I meant a true emergency there. A medical emergency is a matter of time as well, but in regards to this topic, it's not something I would put my crews into a bind with when I know that I have to get that flight back on schedule.

Last I knew there was only one type of an emergency. However, my point was, forward thinking airlines won't build in traps for the crew (pilots and dispatchers) in the MEL. I can find plenty of traps in Boeing and Airbus MMEL that could really bite crews. Having a practical company MEL avoids those pitfalls.
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donniecs
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RE: Ground Spoilers Necessary For Dispatch?

Fri May 08, 2009 4:55 pm



Quoting Fr8Mech (Reply 16):
Ground spoilers can not be deferred, except as individual panels

While not a large aircraft, the GV's entire spoiler system can be MMEL'd. Obviously if possible the AFM says to pull the speed breaks out (30 degrees deflection instead of the 55 in auto mode) on landing. But all landing numbers in the manuals are with full ground spoilers or no spoilers on landing.

Sorry I keep referring to the Gulfstream aircraft (which probably aren't the intended type of ACFT for this discussion or Part 91/135) but that’s my only experience outside of helicopters.
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tdscanuck
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RE: Ground Spoilers Necessary For Dispatch?

Sat May 09, 2009 4:54 am



Quoting Faro (Thread starter):
Can an airliner be dispatched with inoperative ground spoilers if fair weather conditions prevail at destination airfield? Just how efficient are they at retarding ground speed if the brakes do most of the work anyway and impart a significant deceleration just after touchdown?

The brakes are impaired without the spoilers because it takes much longer for full weight to sit on the gear. Depending on the wing incidence angle, it may be impossible to get full weight on the gear without the spoilers when you have significant speed.

Quoting Faro (Reply 3):
Presumably, this facility would only be really necessarily on a wet runway. One would imagine that on a long, dry runway this would not matter as much. Would inop ground spoilers be allowed in such favourable conditions?

No airframer that I'm aware of tests this, so there wouldn't be any available performance data, so no.

Quoting Donniecs (Reply 14):
The Gulfstream GIII, GV and G550 series aircraft can be dispatched with "automatic ground spoilers system" inop, provided the aircraft is operated IAW the AFM limitations, MMEL 27-3 (cat C).

I assume that the manual spoilers have to still be operative in that case, right?

Tom.

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