JRBarrett

Was it a boxed version you bought on Amazon? If so, that version was published by Aerosoft, and you would need to get the update from them.
 
http://www.aerosoft.com

This. The combination of altitude and temperature (if using real weather) at KLAS can lead to very high density altitudes, and that can cause the engine to quit if not leaned. Pull the mixture back a bit, and increase the throttle to bring your RPM up to about 1200. The idle speed in the stock 172 has always seemed a bit low in any case with the throttle fully back.
 
One way to see if the the combination of altitude and temperature is the cause of the problem would be to load the 172 at a sea level airport with real weather off - which should give an air temp of about 60 degrees F. If the engine does not quit in that scenario, then it is definitely being caused by the environmental conditions at KLAS.

Be sure you are not arming the spoilers for auto-deploy before takeoff. Sim pilots who also fly Airbus models sometimes make this mistake. Arming the spoilers IS required before takeoff on the Airbus, but is NOT required on Boeing models.

Runway 36L does not exist in default FSX or P3D at KCLT - it was only opened in 2010. If you were following the extended centerline in LNAV mode using current AIRAC data, it was sending you to where the runway now exists, but indeed, that location was only empty fields in the default sim, (which reflects the way things were before construction of the new runway started).
 
I know there is at least one payware KCLT add-on that may have the new runway, and there are free AFCAD updates here in the AVSIM file library that will add the new runway as well. The one by Ray Smith is likely to be excellent, as he does outstanding work.

This is a known limitation of FSX in replay mode with complex aircraft. PMDG models are not the only ones affected.

What are you trying to calculate? It would be helpful to know what you are using the results of your calculation for.
 
Temperature changes the density altitude primarily, which will indeed be higher than pressure altitude at temperatures above ISA, and lower at temperatures below ISA.
 
Density altitude affects aircraft performance, and is of immediate concern when calculating takeoff power and distance requirements on hot days at higher altitude airports.
 
TRUE altitude is also affected by temperature. Assuming that the pressure is standard (29.92 in/hg / 1013 hp), and your altimeter is set to STD, your actual MSL altitude will be lower than what your altimeter reads when the air is colder. This mainly affects aircraft which have a simple altimeter directly connected to the outside atmosphere with a relatively short static pressure line and have no ADC to correct the altitude readout.
 
True altitude of course is also affected by the current air pressure - whether it is above or below STD. Even a simple altimeter will automatically correct for that when flying below the transition altitude, as long as you have set the correct local barometric pressure.
 
At the flight levels, in a high-performance aircraft, the Air Data Computer automatically corrects your altitude and speed readouts for the current TAT (which varies with your speed).
 
But, to answer your question, yes, if you are trying to calculate true altitude, you will generally add when temps are above ISA, and subtract when it is colder than ISA.
 
Air temps will also affect your indicated airspeed due to changes in the air density, which is why ADC-equipped aircraft use Mach numbers for speed control at higher altitudes. The Mach number is automatically corrected for temperature.

Many airports have regulations discouraging, or outright prohibiting excessive use of the APU when parked at a gate, due to noise and air quality issues, so it is typical for aircraft to connect to ground power as soon as possible after arrival at the gate - and to delay starting the APU on departure until just a few minutes before pushback.
 
For the same reasons, it is typical for aircraft to connect to a ground source of conditioned air when at the gate.
 
PMDG represents ground power and air conditioning as stand-alone gasoline or diesel-powered units on wheels, and while these do exist, it is more typical for power and conditioned air to be part of the gate infrastructure at large airports. The conditioned air is usually supplied by a large HVAC unit mounted on or beneath the jet bridge, and there will also be be permanently mounted power cables for supplying 120 volt, 400 Hz, 3 phase AC power, as well as 28 volt DC power.
 
I would think that airports with a "5 minute" APU rule, have provisions to waive that rule if an aircraft is parked at a gate where ground power or conditioned air is inoperative.

Yep, you're doing it right! It's unfortunate that Carenado did not program any VNAV perf functionality into their FMS - and I doubt that they will ever add that feature. The only option is to hand calculate your own TOD the old fashioned way.

Turn on the two ALTERNATOR switches on the left side of the overhead panel. Carenado has misconfigured these switches to turn the main engine generators off and on. In reality, these switches only control the electrical power source for the heated cockpit windows.
 
Although many of the clickable overhead panel switches appear to have no function in the sim, to emulate actual Hawker procedures, You should set the overhead switches as folows:
 
Before engine start: Fuel Boost pumps on. Engine Computers on. Ignition on. Main Inverters on: Standby Inverter OFF. (Should actually be ARM, but doing so causes a false "STBY INVERTER" caution light.)
 
 
After start: Generators on. Start Master off. Alternators on. Screen Heat on. Pitot Heat on. Ignition off. This should give you a clear master warning panel, with no lights, except "APU On"
 
In real ops, Hawker pilots would typically take off with the APU running, with APU generator off, and bleed air ON, but the underlying reason for doing this is not simulated in the Carenado Hawker, so probably best to turn the APU off after engine start.
 
Finally: After takeoff, turn Main Air Valve switches on: This turns on the engine bleed air supply for cabin heating and pressurization.

There are two separate fire loops for redundancy - Loop A and Loop B - specifically to provide backup fire-sensing case one of the two loops fails in flight. If both loops fail the self-test on the ground, it would be a definite "no fly" item until the loops are repaired. 
The squib is a small explosive cartridge located at the outlet of the pressurized fire extinguisher bottle. A fire extinguisher bottle contains the extinguishing agent (typically halon), pressurized to about 600 psi. There is a sealed metal disk inside the outlet port of the bottle which keeps the contents inside. When the fire extinguisher is activated, 28 volts are applied to the terminals on the squib, which contains an explosive primer similar to that found in a shotgun shell. When the squib explodes, it punches a hole in the sealing disk, which permits the pressurized halon gas rapidly flow out of the extinguisher very rapidly, through a large-diameter pipe, and into the engine cowl, APU enclosure or cargo compartment as the case may be.
 
The electrical continuity of the squibs are constantly monitored by the system. If the continuity on a given squib fails, it means that it likely would not fire when commanded - and would have to be replaced before the aircraft could fly.
 
Another cause of squib electrical continuity test failure would be if it has actually been fired - in which case the related fire extinguisher bottle would be empty. However if a squib is accidentally fired on the ground, usually anyone working in or around the aircraft will immediately know it, as it makes a very loud "bang" when it explodes!

Make sure that "show all variations" is checked in the aircraft selection menu. Also, scroll up to the top of the list, you may find them listed as "Boeing" 737, rather than "PMDG" 737.

The key should be right on the download page for your original purchase under your account at the PMDG website. If you have used up your allowable number of activations, you will have to submit a support ticket with your original order number, and they can reset your activation counter.

The FSX versions of the 777 and NGX will NOT (currently) run under Steam. The aircraft files and folders may install OK, but the flexnet licensing service required to activate the purchase (and keep it activated) is not currently compatible with the Steam version of FSX.
 
Robert Randazzo has posted that PMDG does intend to support Steam, and are working to update their installers to achieve that, but there is not yet a target date. Until that happens, there is no workaround to get the 777 to function in SE.

The PMDG 777 and NGX are not yet compatible with the Steam version of FSX. Flexnet is the service that runs in the background which insures that your PMDG add-on is legally licensed, and that service won't run under Steam yet.
 
PMDG is working on making their newer products compatible with the Steam FSX, but they have not announced a target date for that. Older PMDG add-ons, like the FSX version of the MD-11 WILL work on Steam - at least if installed on a system that does not also have the original FSX installed.