Maximum Gear extended Altitude and problems

[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!

[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?

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.

[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.