Eddie Sez:

What's going on here, I am suggesting you cheat on the performance problem on your next recurrent? No, not at all. I'm just trying to do a better job explaining the process than you are likely to get in the fifteen minutes devoted to this problem. In the days of paper we used to take the G350 section and throw it away. Now, with electrons, you have to make sure you punch the correct icons and trace the lines on the chart correctly.

There are a couple of "gotchas" in the twin engine flight planning charts. I grew up with chasing lines on charts and I still make mistakes on a few of these graphs. In real life I run the flight plan on the FMS or Arinc-Direct. But here's how it is done the old fashioned way.

What follows comes from the sources listed below as well as my comments and techniques shown in blue.

Example Problem

Figure: Example Problem, from FSI Savannah around 2010.

Estimated Landing Weight

Just a little math here:

BOW 43,000
Pax 1,000
Baggage 1,000
Fuel Reserve 4,000
= 49,000

Time En Route

Figure: Twin Engine Flight Planning, from G450 Performance Handbook, page PB-18.

Enter the Range scale with your trip distance and draw a line to the No Wind line, draw another line down to read the en route time of 6 hours even.

Trip Fuel, Takeoff Weight, Initial Flight Level

The next series of answers are arrived at by first continuing the line from time en route (6+00) upwards until the reference line. That line is continued to the left parallel to the lines which slope upwards right to left.

Then draw a line from the landing weight, which does include reserves, (49000 lbs) until it intersects the previous line. These lines intersect just to the left of the "Initial FL 450" line, which means your initial flight level will be something less than that, depending on flight level rules in your region of the world.

Trip Fuel, Takeoff Weight, Initial Flight Level

Of course nobody is going to allow you to fly "just a bit less than FL450." If you are flying west where the hemispheric rules are even until FL400 and the next possible choice is FL430, you would have to settle for FL430. It will obviously take more fuel to cruise at a lower altitude so you will have a higher trip fuel burned.

So we will continue to the left until we reach FL430 to determine trip fuel burned WITHOUT reserves (16500 lbs). By adding reserves (4000 lbs) you then determine trip fuel required (20500 lbs).

Takeoff weight is the landing weight (49000 lbs), plus trip fuel required (16500), minus taxi fuel (400) which equals 65100 lbs.

Rated Takeoff Performance

Figure: G450 Takeoff Planning, Dry Runway, Flaps 20°, APA 2000 Feet, from G450 Performance Handbook, page PA-21.

You need to turn to page PA-21 of the Performance Handbook next:

Note 3 tells you to adjust available field length by 500 feet if the ground spoilers are inoperative, so your Adjusted runway length is 6200 - 500 = 5700 feet.

Chart selection is key here, you must use the chart for 2,000 feet pressure altitude, flaps 20°, and a dry runway. Rounding our weight up to the 66,000 lbs row you find immediately that VSE is 164 and VREF is 145. Going to the right until you reach the 15°C column reveals a required runway of 4850 feet to which is adequate, given our 5,700 feet adjusted runway length. In that same column you find V1 = 127, VR = 135, and V2 = 141.

Going up the column to the top you find an EPR of 1.69.

Flex Takeoff Performance

Figure: G450 Takeoff Planning, Dry Runway, Flaps 20°, APA 2000 Feet, from G450 Performance Handbook, page PA-21.

To find the flex power setting and required runway, take the adjusted runway length of 5700 feet and find the lowest column which permits takeoff at 66000 lbs. That ends up being the column for 35°C where you find your EPR setting will be 1.63 and that results in a required runway of 5680 feet.


Gulfstream G450 Performance Handbook, GAC-AC-G450-OPS-0003, Revision 20, November 30, 2011