Maximum Gear extended Altitude and problems

[Pace]

Really put this in as a discussion point! other than the obvious engine failure scenario but plays a part in moving an aircraft gear extended or failure to retract on a trip.

Pace

[mad_jock]

Sorry mate, I know I am crap at spelling and grammar but I can't figure that one out.

Can you rephrase it please.

[Pace]

MJ

i know the A320 has a maximum gear extension ALTITUDE of 25000 feet.
I cannot find any reference to a Maximum Gear ALTITUDE for the Citation!
I had a situation with a gear leg refusing to retract on a recent trip and had to decide whether to continue with the gear down or divert. I diverted to a maintenance unit who thank fully fixed the problem and we continued 4 hrs later.
That obviously got me thinking about maintenance flights with the gear down and how high the aircraft would climb in such a state etc etc etc.
the gear speed is 250 its IAS and obviously at altitude the IAS would not be that but how would gear extended effect the climb altitude and why do Airbus publish an extension altitude of 25 K AND NOT SAY 30k or 35k etc ???
IE if you were moving a B jet 600 nm for a gear maintenance problem with the gear down how high would you fly the trip? 10K 20k 30k ETC

Pace

[Pace]

Brai

There are the obvious problems of performance engine out and ice accumulation on the extended legs in icing conditions as well as the decrease in speed and high fuel burns at least in my machine :{

Hence theoretically gear down the higher you go the less fuel burn and the higher TAS but how high will you safely go.

Is the 25K reference to the 320 its gear extended ceiling or for other reasons?

Pace

[galaxy flyer]

Depends on the type and any Mach limits on the gear.

GF

[CaptainProp]

Haven't flown the airbus for some years, so correct me if I'm wrong, but I believe Airbus has published graphs up to FL290, in FCOM PRO-SPO, for flights with gear down. FL250 is limit for "normal" ops and is actually a gear door limitation rather than a landing gear limitation.

CP

[Pace]

Captain prop

I am sure you are right and thanks for adding detail
What I am trying to understand are the reasons for those limitations ?
Is it to do with the ceiling being lower with extra drag of gear or other factors?

Pace

[mad_jock]

Could be a mach limit linked with a can't be arsed doing the tests to get it certified.

[south coast]

Most likely a certification issue.

Same as many planes have a flap limitation of not to be extended above 20,000'...if you are within the speed limits, what difference does 20,000' or 20,001' make?

[con-pilot]

Just a couple of things.

On the 727, if the tail skid did not retract the fuel burn pentalty was high, surprisingly high. Can't remember the numbers now, but if on a maximum range misson for weight, you were not going have near enough fuel to make it, requiring an unplanned stop.

I have a good friend that was flying a Westwind II for a Japanese ocean fishing company operating in the Pacific Ocean. He departed Midway Island one day heading for some other island and around two hours into the flight the right main gear came out of the gear well and locked into postion*.

He turned around immeditely and headed back to Midway. They barely made it. They could not stay at altitude, 410, and the fuel burn was atrocious. About an hour out of Midway on the return a Coast Guard C-130 joined up with them. He said seeing the C-130 gave them some security, but really didn't think that the Coast Guard would be able to do much for them if they had to ditch with either the right main down or all the gear down, which he decided would be most survivable. But at least the Coast Guard could tell his family the spot he was killed at.

Never the less they landed back at Midway on fumes**. He quit that job and came back to the US, think he is flying a G-V now.


* On Westwind aircraft trapped hydraulic fluid, in a short line, is the main grear up-lock, that line split, all the trapped hydraulic fluid leaked out and the gear came out and free fell into postion. At least that was the way it was 20 years ago, don't if that has changed now or not.

** For those here that are familar with the Westwind II, he had the aux baggage fuel tank installed and filled. If not for that aux tank, they would not have made it back to Midway, that was how close it was of them not making Midway. That'll sober one up. I think he told me that they had less than 50 gallons of fuel left when they filled up the aircraft after the line was replaced and they headed to PHNL.


Just glad it wasn't me that this happend to when I flew a Westwind II from SFO to PHNL a few times back when I was young, bullet proof and hungry. :uhoh:

[wiggywoo]

Hi Pace.

Don't be fooled into thinking that ALL limitations are structural, performance, controllability or aerodynamic related: sometimes the limitation can be set simply by how far they were required/bothered to test it.

F'rinstance, one of the aircraft I am involved with (Phenom 100) has a max altitude limit for flaps extended of (if I remember correctly) 12,000' YD off and 15,000' YD on. Having spent considerable time trying rationalise this we were informed that these were simply the altitudes to which the certification pilots successfully flew before putting a tick in the box - which raises the question "why not tick the box at the same altitude"? There was no answer, just a shoulder shrug.

Pure speculation of course, but maybe for your Citation they flew the aircraft gear-down to max operating altitude before putting the tick in the box but for your Airbus they put the tick in the box at 25,000', having no requirement to test further. Is anyone LIKELY to want to fly an Airbus gear-down at, say, 38,000'?

Clearly, I don't KNOW the answer to your query, but just offer this explanation as a reasonable possibility which appears to have not been considered so far.

Wiggy.

[lifeafteraviation]

I think if you are in a part 121 environment the only choice would be to burn down to landing fuel and land as soon as practicable. I think it's highly unlikely you can amend your dispatch release in such a scenario. The most conservative choice is almost always the one to make.

If you are part 135 you should consider what is the safest course of action for your passengers but you have a bit more discretion to make that decision. The end result usually determines the wisdom of your decision. Hindsight is 20/20 so to speak....if you survive and don't cause further damage or incident, your decision was sound enough.

If you are part 91 that logic extends a bit further.

Basically be prepared to be judged by the outcome....if you elect to burn down to landing fuel and land and lose the revenue from the flight you may be asked about why you didn't continue. If you continue to your destination, land, and collect the revenue from the flight but have stranded the airplane to the point it must now be ferried all the way back at high cost you will likely be blamed for wasting money too. If you continued a revenue flight that also brought you back to or closer to a maintenance base you may get a big pat on the back, a heroes welcome by management, and paraded in front of the other pilots as a shining example of a team player.

As far as the technical side of it....your FMS will probably tell you what your landing fuel will be based on the new airspeed and power settings or you can easily enough calculate it...don't cut yourself short thought. Some airplanes publish limitations on this and some don't...know your limitations and comply with them.

Basically use your judgement, this is what we get paid to do. And as I might point out...this is what sets an experienced pilot apart from an inexperienced one...it is also one of those moments that defines your experience.

[Pace]

LifeAfterAviation

My decision was to divert to a close airport with a major Cessna service centre and that was the right call basically because the problem was fixed and we continued some 4 hours later.

But this got me thinking about how I would plan a flight with the gear down had I had to move it empty some 600 nm?

On a 600 nm flight I would normally be up at FL360/370 what would I do with the gear down?

What level would I fly at? If there was weather ahead would I still stay low or climb over the weather?

would i stay relatively low and accept the high fuel burns especially with higher N1 against drag or go higher gear down and get lower fuel burns and higher TAS?

Infact compared to clean how high could I go ?

Pace

[dc9-32]

ATR72 gear down ferry is limited by altitude (max FL100) and a reduction in the MTOW to 17556kgs.

In the A310 FCOM Special operations, there is the determination of the MTOW. It states a variety of weights for different configurations and serial numbers.

[lifeafteraviation]

There is no way to calculate performance during cruise with one or more gear extended unless for some reason your AFM provides it.

You simply have to start cruising and see what the plane will do....

Chances are you can't land anyway because you are overweight so you have some time to figure it out.

If you are heading out over land with plenty of viable alternates along the way this isn't so much of a problem. If you are headed out over open water or hostile land forget about it.

If there is a good maintenance base on the way you can use as a contingency before having to make the final decision that's even better.

[3 Point]

Be very careful!

"your FMS will probably tell you what your landing fuel will be based on the new airspeed and power settings or you can easily enough calculate it"

This is exactly the cause of the Airbus 300 which ran out of fuel at Vienna in 2000

Hapag-Lloyd Flight 3378 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Hapag-Lloyd_Flight_3378)

The FMS will possibly not have the capability to use the actual fuel burn figures, it may use programmed data which will not be accurate!

Happy landings

3 Point

[Denti]

The gear down long range cruise altitude capability tables for my 737 go up to a pressure altitude of 39700. The main concern here is residual climb capability of 100 fpm at that altitude with max cruise thrust. There is no altitude limit for gear extension, just a speed limit of M .82 and 320kias once its extended. Fuel flow tables only go up as far as FL370 though.

Nothing special required for gear down ferry flights, any normal line pilot can do that, just get out the QRH and check the fuel tables. FMC fuel predictions can not be used though.

[Pace]

Denti

That is interesting information on the 737 but cannot find anything published for a Citation :uhoh:

3 point

Hapag-Lloyd Flight 3378 (HF-3378), registered as D-AHLB, was a commercial Hapag-Lloyd Flug Airbus A310-304 flight, on 12 July 2000. It was carrying 142 passengers and 8 crew members from Chania, Greece to Hannover, Germany.

The flight departed at 10:59, after which it was noticed that it was not possible to retract the landing gear fully. Using the Flight Management System (FMS), the crew estimated the aircraft's fuel consumption and the captain decided to shorten the flight and land in Munich. There was not sufficient fuel to reach Munich, however, as the FMS was not designed to take into account the extra drag produced by a half-raised landing gear. After an alarm at 12:49 informed the crew that there was only 1.3 metric tons of jet fuel left in the tanks, the pilot quickly redirected the flight to Vienna, 120 nm (220 km) distant, although Zagreb was closer at 40 nm (75 km). The aircraft ran out of fuel twenty kilometers (12.4 miles) before Vienna and the crew were left to glide the jet towards the runway. It touched down 500 meters (1,640 feet) short, striking airport equipment, spinning 120 degrees, and coming to rest off the runway. Some of the passengers were injured, although none seriously. The aircraft was written off due to the severe damage caused to the underside of the fuselage.[1]

Fuel burn would be the reason to go high

Pace

[Denti]

If there is a pretty obvious restriction like that on the airbus wouldn't it be in the limitations section of your FCOM? At least that's what i'd expect.

If there's nothing than there is no limit, hence you could go up max ceiling if you really wish to.

[3 Point]

Pace,

I know what the Wikepedia article says; I read it before I posted the link!

My point is that readers should use caution with liferaft saying that the FMS will tell you the expected landing fuel. In the Hapag-Lloyd incident the crew relied on the FMS fuel calculations but were not aware that it was using stored date for clean cruise configuration at the actual altitude and speed they were flying hence they overestimated their max possible range and ran out of fuel before their planned landing airport!

There was not sufficient fuel to reach Munich, however, as the FMS was not designed to take into account the extra drag produced by a half-raised landing gear.


I was flying the Airbus when this accident happened and I recall we were all briefed and shown in our next sim how the FMS fuel calculations were inaccurate during gear down cruise.

That's all; just saying be careful out there!!

3 Point

[lifeafteraviation]

Be very careful!

"your FMS will probably tell you what your landing fuel will be based on the new airspeed and power settings or you can easily enough calculate it"

This is exactly the cause of the Airbus 300 which ran out of fuel at Vienna in 2000

You're right and that's a very good point. High end FMS systems such as found in airliners use more complex algorithms to calculate estimated fuel burn and draw from a database created from the AFM as well as winds aloft, climb, descent, and approach. In that case the Airbus crew should have know this.

Having some background here I was making he assumption that the Citation may have had something like an older Universal or older Honeywell that calculated fuel burn based on current conditions only....so that on a typical long range flight it shows zero fuel on arrival for the first half of the flight until you start "making fuel."

Always be familiar with the capabilities and nature of your aircraft and it's optional equipment.

In either case, you can use the FMS to calculate within the criteria noted above.

Also....as long as there is no altitude restriction on gear extended operation for the particular aircraft, it would be in your best interest to climb as high as you can to reduce fuel burn and obtain a higher true airspeed because your gear extended limitation speed must be observed but that's based on indicated, not true.

and...

Knowing Airbus...after this happened they probably just programmed a new sensor to allow the FMS to detect a gear down condition and adjust accordingly...thus making the plane as idiot proof as possible! :8

[Pace]

LAA

The Citation struggles in the mid to high 30s even clean IAS maybe back at 170 KT coaxing a slow climb! Just imagine dropping the gear in that situation,climb rate would disappear airspeed would drop and the only way would be down but down to what? My guess is nowhere near the clean level for a given weight

Pace

[Denti]

Knowing Airbus...after this happened they probably just programmed a new sensor to allow the FMS to detect a gear down condition and adjust accordingly...thus making the plane as idiot proof as possible!

Nah, they just did what any sensible OEM would do, add a note in the FCOM that the FMC fuel prediction shouldn't be used with gear down :)

[CL300]

it comes back from CAR 4 certification rules, and carried on FAR25 and CS25. The aerodynamic rules are changing around 20000 ft, leading to different formulas for compressibility computations.
Therefore you will find a lot of numbers around 200 kt and FL 200, just for this reason. Now, nothing prevents a manufacturer to test fly and expand data sets ( like the 10kt tailwind limitation, this is a minimum available for ANY FAR25 airplane, but some can have a wider range and go to 20kt)

CS25 or FAR 25 is the minimum textbook performance and handling, if you can do better..just do it !

[Pace]

CL300
if you can do better..just do it !

Coffin corner would stop me trying it at too high a flight level :{ all a bit test pilot stuff

Pace

[M-ONGO]

Coffin corner would stop me trying it at too high a flight level all a bit test pilot stuff

Do you worry about coffin corner in those little Cessnas?:O

PS, my type is certified to FL200 for slats, flaps and gear 'operation'.

[Pace]

I would do in the mid higher 30s when in the slowtation you often clean have to level then step climb the last couple of thousand feet :{
20 s sounds more realistic

Pace

[Empty Cruise]

WRT use of the FMS and predicted fuel....

Well, how about you plug in the IAS you can achieve for cruise, see how long it's gonna take you to get to where you're going - and then multiply with the fuel flow... That's not exactly rocket science.

A bigger issue is whether you will be able to go missed with the gear down, especially if an engine rolls over and dies. Reduced flap landing may be prudent, as would burning down fuel before commencing the approach.

Enroute terrain clearance would also be a massive issue. Without a "Dispatch with the Landing Gear Down" supplement, I'd be careful about what assumptions I'd make.

That being said - if the gear doesn't retract after T/O (rather than a dispatch) - gain as much altitude as possible while sorting it out and formulating a plan. You can always descend later, but you're only going to gain altitude while multiple engines are operating. Once you're down to one, your options become limited.

[lifeafteraviation]

You know...if you have a gear retraction problem....it's very possible it's just one gear or a stuck door even....your performance may be good enough that it's difficult to even notice except for the red light on your panel....until you get high enough that it's noticeable or you go fast enough that you can feel it.

"Coffin corner" wouldn't be an issue, that's something else entirely and usually not something you think about with modern computer designed wings and not in a straight wing Citation.

[Pace]

LifeAfterAviation

Correct me if I am wrong but I always thought that coffin corner was where the critical Mach number and stall speed met?
The U2 was also a straight winged jet but operated in that zone to such an extent that the only way to fly was on autopilot?
Why do you say the citation which is a straight winged jet will not experience those problems?

"Coffin corner" wouldn't be an issue, that's something else entirely and usually not something you think about with modern computer designed wings and not in a straight wing Citation.


Pace

[jetdriverbr]

To the OP or any Citation driver,

If you need data for a ferry flight, usually this requires a call to Cessna. I had to ferry our 680 because of a flap problem. The AFM did not have any numbers for no flap takeoff. Cessna had to send tables, which were forwarded to the FSDO issuing the ferry permit. The FSDO balked because they were dry numbers, but it was wet. Long story short, by the time Cessna got us wet numbers for a flaps clean takeoff, it was dry!

[lifeafteraviation]

Correct me if I am wrong but I always thought that coffin corner was where the critical Mach number and stall speed met?
The U2 was also a straight winged jet but operated in that zone to such an extent that the only way to fly was on autopilot?
Why do you say the citation which is a straight winged jet will not experience those problems?

You are correct in your definition of "coffin corner."

But...

Critical Mach number in a modern jet is higher than your Mmo and with a properly designed wing the effects of exceeding it will be diminished compared to older jets...not to mention all the bells and warnings you will hear before you get there. Also, the stall speed of a modern, properly designed wing is much lower even during high altitude cruise so the operating envelope can be very wide even at FL410...thus you should never approach "coffin corner" even at max certified altitude.

For example, the "coffin corner" of a particular modern jet might be a problem at over fifty thousand feet while the aircraft is only certified to operate forty one thousand and you may be hard pressed to climb even that high under normal conditions.

The SR71 operated at around seventy thousand feet and had high performance engines to take it there. Yes, such airplanes are very difficult to fly by hand under those conditions. A Learjet 20 series operating at forty five to fifty thousand feet for example....an old jet with a less than well designed wing (by modern standards) was very difficult to hand fly and you had only a few knots to work with sometimes.

If you are limited in performance by having one of all of your gear extended you would be forced to operate at a lower altitude and lower airspeed. Stall speed may be a concern if you push your altitude too hard at a low airspeed (some guys stalled and crashed a CRJ way back by trying to push it to FL410) but over speeding would be more difficult especially if you adhere to the gear extended speed limit of the AFM.

This is why I say "coffin corner" would not be an issue in the context of this discussion. Hope that helps. :8

[lifeafteraviation]

To the OP or any Citation driver,

If you need data for a ferry flight, usually this requires a call to Cessna.

This is a good point. Although you don't need a ferry permit if the problem occurs during that flight (can't land and then take off again knowing you have a problem), you can use a satellite phone and call the manufacturer during flight.