KM732
Topic Author
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Why Sometimes No Gear Retraction After Take Off?

Tue Jul 08, 2003 6:42 pm

Hi all!

Maybe you´ve seen something like this, too: Just yesterday I saw
a BA A320-200 climbing out of MUC´s RWY 26R which didn´t retract the gear until she was about 400-500 meters (approx. 1500ft) in the air.

I´ve seen this on many others before: BA ERJ-145, LH A300, Syrian 747SP, Royal Jordanian A320, ....

Now why is this? Answers I´ve gotten so far range from the pilots being too busy with ATC and flying or the need for cooling the brakes....

Maybe somebody knows! I always thought that "Positive Rate of Climb - Gear up" is the one of the first things to do after Take Off!



Thanks for any ideas!



Stefan
 
Klaus
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 08, 2003 6:59 pm

Cooling the brakes seems to be one popular reason...
 
Yikes!
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 08, 2003 7:26 pm

Twice in the last 10 years I watched first a C3 B757 leave the gear down until it was well out of sight, departing Halifax and just 6 months ago a Lan Chile 763 departing Cancun. The second one was visible for nearly 5 minutes after departure as it took off RW30 then made a long right turn out in the opposite direction. The gear stayed down for as long as I watched, which was until it disappeared from view. Might have even been longer than 5 minutes.

I'm not too sure about the brake cooling (I'm going to call it a myth) as they are going to cool very quickly anyway.

Hope others can jump in. So far my opinion is simple. Gear retraction was simply forgotten perhaps by reason of a distraction.
 
broke
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RE: Why Sometimes No Gear Retraction After Take Of

Tue Jul 08, 2003 8:23 pm

There are fire warning loops in the wheel wells, on most airliners, to detect overheating or a fire in the landing gear, usually caused by the brakes. If either of there loops are inoperative, the MEL (Minimum Equipment List) would require that the landing gear be left down for a period of time after take-off for cooling in order to dispatch the airplane.
 
Guest

RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 08, 2003 9:22 pm

Cooling the brakes is sometimes done by leaving the gear down after takeoff, has to be done occasionally after long taxi - or after a few landings and touch and goes in training, leave the gear down for a circuit, every 3 or 4 landings. Brakes cool fast in the airstream, but in the wheel well, takes a long time, and if overheated brakes, tire may explode, and damage other aircraft systems. Remember the Nationair DC8 in Jeddah - 1991 or 1992...
xxx
I have yet to see airline pilots "forgetting the gear" after takeoff - the call of "positive rate" which is standard for 99% of the airlines is a trigger for a call "gear UP..." - the only other reason is brakes cooling, I dont know any other, in any airplane...
(s) Skipper
 
Yikes!
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 08, 2003 10:21 pm

Reasonable reasons. The accident in Jeddah though was much more insidious than overheated brakes. The two aft tires on the left (I think) bogey disintegrated very early on the takeoff roll. The tires shredded and much of the takeoff was continued on the remaining rims which eventually wore down to the axle. In fact, the axle itself looked like a "D" - they were shaved flat.

And Red Hot. During retraction another tire exploded in the wheel well severing bleed and hydraulic lines.

Then things really started to fall apart.

I unfortunately have indeed seen and heard stories of pilots forgetting to raise the gear on departure.

Just a few more thoughts on the original question.
 
clrd2go
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 12:13 am


When I lived in Phoenix, 20 something years ago, I used to see this frequently
as aircraft departed Sky Harbor, particularly during the summer.



Jim
What a long strange trip it's been
 
kellmark
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 12:18 am

Occasionally an aircraft has a hydraulic failure and is unable to retract the gear. Or in cold climates it has been known to have a gear freeze in position. There are also times when an aircraft is ferried to maintenance with the gear down. Also some aircraft such as the L-1011, have items which could be inoperative which can affect the speed of gear retraction. On that aircraft there is a bleed air driven turbine motor which helps the hydraulics raise the gear rapidly. If it is inoperative there is a much slower gear retraction, but a performance penalty is applied to make up for it.

Most of the time, if there is a late gear retraction, then it is a pilot decision for brake cooling, as was stated, or an oversight.

I have also seen that sometimes when an aircraft makes a go around they leave the gear down until they come back around, but that is not a usual recommended procedure.

It is difficult to reconcile a crew leaving the gear down for an extended period without noticing. The aircraft's performance is significantly affected and the noise level is much greater in the aircraft. The nose gear is usually right under the cockpit.

Pilots need to keep in mind that if they leave the gear down, then their second segment climb performance is greatly reduced if an engine fails.
 
KM732
Topic Author
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 2:20 am

Thanks for all your replies  Big thumbs up! It was very interesting to finally find out about this!


Kind regards, Stefan
 
Rick767
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 6:37 am

We get this sometimes if a brake is "capped off" meaning the wheel might continue spinning after take-off. We must leave the gear down for 2 minutes to allow for this.

For a Flap 15 take-off (752) the second segment climb limit weight is reduced by 14,300kg, pretty restrictive but not usually a problem on shorter Euro runs so we can normally keep all the bags and SLF!

Only ever done this once in 4 years. Tecchies can refer to B757 MEL 32-41-1.
I used to love the smell of Jet-A in the morning...
 
air2gxs
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 7:44 am

When brakes (up to 2) are removed from a 747 aircraft the MEL says you must keep the gear down for 2 minutes after take-off in order for the wheels to stop spinning. The last thing you want is that spinning mass entering a wheel well full of hydraulic lines.
 
Guest

RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 8:46 am

Absolutely correct for capped brakes...
What we also do, taking off in snow or slush, is to leave the gear down to "clean it" before retraction. Some guys retract, then again cycle the gear briefly... down and up finally...
xxx
(s) Skipper
 
aaron atp
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More Useless Info For Deactivated Brakes...

Wed Jul 09, 2003 10:09 am


...for those who are interested

tailwind takeoffs are often not authorized, RATOW is reduced, max quick turn weight is reduced, and runway allowable landing wt is reduced.

and sometimes, no reduced power takeoffs or CAT III approaches, depending on the AC...

IIRC, many dispatch requirements vary depending on whether the brake is deactivated with a antiskid shuttle valve plug or if the line is capped.

(nothing new for most of you, just tidbits for the interested)
aaron
 
MxCtrlr
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 09, 2003 11:54 am

Brake cooling for MEL purposes is only one reason to purposely leave the gear down for an extended period after take-off.

The other valid reason is because the aircraft was fueled previously (possibly for a different route) and, if no defueling truck was available in a timely fashion, the airlines' operations dispatch center may choose to fly for a period of time to burn off excess fuel. I have actually seen this happen and it is not as uncommon as one might think.

MxCtrlr  Smile/happy/getting dizzy
Freight Dogs Anonymous - O.O.T.S.K.  Smokin cool
DAMN! This SUCKS! I just had to go to the next higher age bracket in my profile! :-(
 
Arrow
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RE: Why Sometimes No Gear Retraction After Take Of

Thu Jul 10, 2003 6:40 am

Forgive me if this sounds stupid -- but why would the brakes get so hot on taxi and take-off that they need to be cooled down? If they can dissipate the heat generated on the landing roll, at pretty high speeds, surely taxiing would be a piece of cake. And why would there be any brake heat generated on a take-off?

Never let the facts get in the way of a good story.
 
HAL
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RE: Why Sometimes No Gear Retraction After Take Off?

Thu Jul 10, 2003 7:08 am

I would believe that by far the most common reason is brake cooling. During taxi you have to ride the brakes a LOT, because even at idle the thrust of most planes (like the 767 I fly) will get you moving at quite a clip. So during an extra long taxi like in HNL to the reef runway, or during hot weather, you can build up a lot of heat in the brakes. Here is an excerpt from our 767 Flight Crew Operating Manual on the subject:

During warm weather on short flight segments of less than about an hour, or after long taxi, the brakes may not adequately cool with the gear retracted. An efficient method of cooling is to leave them extended for a period after takeoff, assuming no engine failure occurs and no obstacle clearance problem exists during the takeoff. An alternate method to improve brake cooling is to extend the gear earlier on approach.

This is in the 'Normals' section of the manual, so it is not considered unusual to do.

HAL
One smooth landing is skill. Two in a row is luck. Three in a row and someone is lying.
 
XXXX10
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RE: Why Sometimes No Gear Retraction After Take Off?

Sun Jul 20, 2003 10:27 pm

Off topic (slightly)
When the gear is left down for a few minutes does this need a change in the briefing,

I would imagine that most PNF's are expecting to hear the 'gear-up' command as soon as they announce 'positive climb'
 
delta-flyer
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RE: Why Sometimes No Gear Retraction After Take Off?

Mon Jul 21, 2003 3:26 am

Arrow....my question exactly! Why would the brakes get hot after taxi? Even after a touch-and-go, the brakes are not used so should not get hot. If the brake can dissipate the energy of the aircraft decelating from landing speed to zero, even with no flaps, sploilers, etc., I don't see the brake cooling argument at all.

It's conceivable that the tires get hot during take-off, but how is one take-off different from another? Why can you retract the gear quickly in one instance, but elect to wait in another? What are the decision criteria?

The only reasons I can fathom for delaying gear up are a malfunction of some sort or an error of some sort.

Pete
"In God we trust, everyone else bring data"
 
covert
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RE: Why Sometimes No Gear Retraction After Take Off?

Mon Jul 21, 2003 6:58 am

Don't know that much about airplanes, but sometimes automobile brakes tend to ride the rotors by thousanths of a centimeter even when not applied, usually when new. Have you ever smelled "new brakes" before?
none
 
aaron atp
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Delta-flyer

Mon Jul 21, 2003 8:30 am

The only reasons I can fathom for delaying gear up are a malfunction of some sort or an error of some sort.

Survey says... errrnt, wrong answer.

Brakes get VERY hot during takeoff, landing, and taxi. It's the simple physics of energy dissipation. Aside from that, tires get quite hot just from the rolling action/deformation as the contact patch deforms (traction waves form at higher speeds).

Stopping a an aircraft requires converting virtually every bit of kinetic energy (1/2 * mass * velocity squared) into heat energy. Even at lower speeds, a 450,000 lb aircraft has quite a bit of KE, and to maintain a slow taxi speed, the brakes must dissipate quite a bit of energy generated by idle thrust. In the newer gulfstreams we would taxi with the buckets out on one engine just to keep the brakes cool. This wouldn't be a problem if the aircraft were on the ground for 6 hours after each flight, but when you qt an aircraft, the brakes don't have time to cool completely.

I don't see the brake cooling argument at all.
Quick-turn landing weights are published to determine minimum turn-around times for a given weight, because the brakes must be cool enough in time for the next takeoff. Otherwise, they will overtemp and quite probably catch fire or at least be damaged in the event of an aborted takeoff (at a minimum they will melt the thermal plugs).

What are the decision criteria?
We have a BTMS (brake temp monitoring system) and published brake cooling procedures based on weight, wind, OAT, pressure altitude, and event (eg. RTO, max manual brake, autobrake 1-4-max, reverse/not).

We add 1 million ft.lbs per brake per taxi mile!
Is that enough to get the brakes hot?

Specified inflight cooling times range from 1 to 8 minutes. With regards to the comment by HAL, our brake cooling charts are in the abnormal section.

[Edited 2003-07-21 01:36:05]
 
delta-flyer
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RE: Why Sometimes No Gear Retraction After Take Off?

Mon Jul 21, 2003 9:22 pm

Aaron......in principle, you are right, but the numbers don't add up. You say things like ....

Brakes get VERY hot during takeoff, landing, and taxi. It's the simple physics of energy dissipation.
How many times and from what speed do you decelarate during taxi? The KE in a 150 kts landing is 25 times (assuming the same mass) that from a 30 kts taxi run, and the former is accomplished over just a few seconds. A long taxi out with maybe 5 stops from 30 kts can take 10-15 minutes, allowing ample time for cooling.

In any event, how hot is hot? 120F is hot to the touch, but 400F may be OK for the brake.

We add 1 million ft.lbs per brake per taxi mile! Is that enough to get the brakes hot?
You tell me -- show me the math. I just a quick check .... to stop a 200,000 pound aircraft from a speed of 200 ft/sec (about 120 kts) is about 125 million foot-pounds -- and that's what the brake is designed to do.
(KE = 1/2 m v^2 ...
m = (200,000 lbmass/ 32.2 ft/s^2) = 6,200 slugs
v = 200 ft/sec)

Sometimes a couple of minutes of simple analysis can put things more clearly into perspective.

Cheers,
Pete
"In God we trust, everyone else bring data"
 
buckfifty
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RE: Why Sometimes No Gear Retraction After Take Off?

Mon Jul 21, 2003 11:42 pm

Not a physics expert, but I'll give it a try anyway.

I think it's fair to say that most brake overheats and fires occur during taxying. And when brake fires occur, it's usually not because the actual pad or disk is on fire, but something else (like melting tires or grease).

During landing, the brakes are cooled by air which flows at high speed around the undercarriage, and the heat dissipates more rapidly. However, during taxying, at slower speeds with long durations of brake applications, heat can build up in the discs in a very discernible way. And considering that the brakes themselves are recessed well inside the wheels on most modern airliners, this heat buildup can ignite flammable materials very easily.

Fusible plugs on the wheels are designed so that they melt under such intense temperatures, and offers two effects a) deflating the tire to reduce the pressure, and lessen the chance of an explosion, and b) the escaping nitrogen will help put out the fire.
 
aaron atp
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Delta-flyer

Tue Jul 22, 2003 12:48 am

We are not talking about the first flight of the morning departing the gate, but first, a landing at some airport with the brakes initially cool and taxi to the ramp (with 5000 lbs of idle thrust to dissipate). That we agree, is enough to get the brakes quite hot, but within their limitations. If we are at a hot and high airport landing heavy, the brakes need a long time to cool. If it is a quickturn, the brakes have hardly cooled, and the taxi back out will heat them up quite bit (likely by as much as they have cooled since stopping at the gate).

Now, the brakes are still capable of stopping the airplane in the event of a RTO, but the thermal plugs WILL melt as the heat soaks through. Assuming the takeoff is successful, do you want brakes that may be well in excess of 300° C inside the gear bay under your seat?

To summarize, we are talking about the cumulative effect of landing, taxiing in, and taxiing back out for T/O in a short length of time.

This is what makes the brakes require inflight cooling.
 
aaron atp
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 22, 2003 12:51 am

 
delta-flyer
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 22, 2003 3:06 am

Aaron....Useful nomograph...thanks.

I agree that if the aircraft has landed a short time earlier, there may not be enough ground time for the brakes to cool. But the heat added during taxi is very small compared to the capacity of the brakes. 1 million ft-lb (your number), compared to 30-60 million? I still have a hard time accepting that taxiing has much impact on brake temp.

If you only add 1 million ft-lb during taxi, then, from the nomograph, it only requires about 4 minutes of ground cooling. This is accomplished during the time spent taxiing, particulary if you have to stop and wait. So, at the end of the taxi, the brake may be at most the same temperature as when it left the gate. The biggest factor is the condition of the previous landing and the amount of time spent on the ground.

Pete
"In God we trust, everyone else bring data"
 
aaron atp
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 22, 2003 5:30 am

Time spent taxiing is not considered in ground cooling times, and taxi distances quite often exceed 1 mile.

So, at the end of the taxi, the brake may be at most the same temperature as when it left the gate.
I don't agree with that.

Because of the time it takes for heat soak to occur, high BTMS temps may even occur after takeoff, and the gear are to be re-extended to allow cooling if you get a brake temp EICAS msg.

Please realize that I'm not trying to make you believe the brakes get too hot every cycle. This deals primarily with landing heavy and trying to make a quickturn, or a TO soon after an RTO; especially at hot/high airports.


The biggest factor is the condition of the previous landing and the amount of time spent on the ground.
absolutely correct.


g'day,
aaron
 
delta-flyer
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 22, 2003 9:09 pm

Time spent taxiing is not considered in ground cooling times....
That may very well be true, but that does not make this effect immune from the laws of physics. Not considering this time as cooling is a good practical assumption, taking into account that the rate at which heat is generated while taxiing more or less balances the brake's capacity for cooling during the taxi itself.

My only point all along was (and is) that taxiing alone does not generate enough heat to require in-flight cooling. The chart you presented bears that out, as the in-flight cooling is only dependant on the previous landing and ground time. I'm glad we at least agree on that!  Smile

Pete
"In God we trust, everyone else bring data"
 
aaron atp
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RE: Why Sometimes No Gear Retraction After Take Off?

Tue Jul 22, 2003 11:30 pm

OK, I think we are seeing almost eye to eye, but one of the notes for the above figure was indeed a requirement that 1 million ft.lb be added per brake/taxi mile. In a normal taxi, the brakes are certainly not ridden, but 98% of the time I think the brakes are quite a bit hotter after the taxi than before.

My only point all along was (and is) that taxiing alone does not generate enough heat to require in-flight cooling.
also absolutely correct

not to drag this out, but this is the quote that got me started on this...
The only reasons I can fathom for delaying gear up are a malfunction of some sort or an error of some sort
If you left the gate with cold iron, very true; but we've both established that heat from previous landings/rto's preclude this.
 
delta-flyer
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 23, 2003 2:17 am

....are a malfunction of some sort or an error of some sort
OK, I guess I did say that....I wasn't thinking of a quick turn-around.

Pete
"In God we trust, everyone else bring data"
 
jetdoctor
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RE: Why Sometimes No Gear Retraction After Take Off?

Wed Jul 23, 2003 1:38 pm

MxCtrlr stated earlier that the landing gear may be left extended to increase the drag, and increase fuel burn. I have also seen this been done, and was just recently on a flight that the crew elected to do this procedure.

The gear was left down for almost 5 minutes after take-off

Jetdoctor
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