13,500+ feet ASL...!!
In a piston prop!
WOWZERS..!
An excellent opportunity to practice your engine management skills.... [smiley=thumbsup.gif]...!
Careful adjustments to the Throttle, Propeller, and Mixture controls to obtain the optimum/maximum power/speed from the engine(s)...

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Don't forget that over 5,000 feet ASL you need to gradually weaken the mixture to get the correct fuel/air ratio for maximum power...:...!
Keep a wary eye on the Engine RPM gauge, Fuel flow gauge, Suction gauge, Exhaust gas and Cylinder head temperature gauges...
...and not forgetting the Air Speed Gauge...

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...and still look where you are going...

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Busy times...

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The Beech Baron should cope with the high altitude just fine with a bit of control tweaking...

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I will try the Cessna 182RG (Retractable Gear) for a change, similar controls (and speed) to the Baron, but only one engine to worry about...

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Paul...G-BPLF... 8-)...!
..and an obvious tip?
If you intend using the Autopilot after take-off, check your airfield's altitude
before taking off!, and set the climb altitude to be GREATER than the airfield's altitude!, (and a positive rate of climb in FPM), beforehand!
...otherwise your propeller may be buried in the ground, and the Insurance Man will be knocking on your door...trust me...

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LOL...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.