E175 Optimal Climb Speeds
Intro
The E175 has a slower climb speed than most other passenger jets. If your operation has default climb speeds like 270/.73 or 280/.74, chances are you’re spending a lot of time in thicker, warmer air in the climb, and burning more fuel as a consequence. Selecting a slower climb speed allows you to have a steeper climb, thus getting you to that thin, cooler air where the engines are more efficient and your TAS is faster, saving fuel and costing only minimal time. Using these climb speeds will save you 100-400 lbs of fuel per segment, which, depending on your planned segment burn, translates to 1-5% savings. That’s about half of the gain that Embraer got from putting on the new winglets.
If you started your flying career in 172s and Seminoles, chances are you have speeds like 74 KIAS and 88 KIAS seared into your memory, along with sayings like “Speed is life, altitude is life insurance,” “Blue line means life, read line means death,” and so forth. If someone asked you for Vy in the E175, you might tell them “Green dot+50,” but maybe not with the same conviction. Green+50 is a useful approximation at low altitudes, but falls apart as you get higher up the climb. Fortunately, there’s a better way.
If you started your flying career in 172s and Seminoles, chances are you have speeds like 74 KIAS and 88 KIAS seared into your memory, along with sayings like “Speed is life, altitude is life insurance,” “Blue line means life, read line means death,” and so forth. If someone asked you for Vy in the E175, you might tell them “Green dot+50,” but maybe not with the same conviction. Green+50 is a useful approximation at low altitudes, but falls apart as you get higher up the climb. Fortunately, there’s a better way.
A steeper climb at a slower speed will save fuel by getting you into thinner air faster.
How to use optimal climb speeds
Hidden away on page 6-10 of the AOM Volume 1 is a table that gives you best climb rate speeds at a variety of weights. You’ll notice that the speed decreases with each 5,000-foot increment, thus showing the “Green+50” rule to fall apart. Once the speeds intercept .63, we’re supposed to do .63 or green dot, whichever is faster. A word of caution: if it’s bumpy, you will want to add some buffer to that, so I usually start with .65 and adjust.
Best Economy Technique
If you’re going for best economy, pick the column that best corresponds to your weight that day, and the altitude that you’ll plan to be after you clean up from your departure. Often, it’s around 240 KIAS. Put 240/.65 in your PERF INIT climb speeds to start with, then on climbout, go manual speeds and adjust the speed to the best interpolation of the climb speeds in the AOM table. Usually, it works out to about 1 KIAS/1000 feet. When you get to the slowest published number up in the 30s or .63 intercept (faster if bumpy), ensure that it remains in Mach until level-off. As you get to level-off and see ASEL on your scoreboard, flick the selector to FMS speeds so that it can accelerate to your cruise speed without throttling back first. Depending on the conditions, you will have just saved 100-400 lbs on your climb burn vs 280/.74. Due to your level-off occurring earlier, your cruise will be a bit longer, so some of the climb savings will go to a longer cruise segment, but you should be 100-200 lbs up from plan at your first post-ToC waypoint under most circumstances.
20/80 Technique
If you want to get 80% of the output for 20% of the work (e.g. short flight, briefing to do, lazy on last leg, etc.), just put 240/.65 in the box and let it do its thing. If it’s bumpy up high or you’re heavy, make the transition at .67-.70 or as appropriate for your cruise altitude.
Best Economy Technique
If you’re going for best economy, pick the column that best corresponds to your weight that day, and the altitude that you’ll plan to be after you clean up from your departure. Often, it’s around 240 KIAS. Put 240/.65 in your PERF INIT climb speeds to start with, then on climbout, go manual speeds and adjust the speed to the best interpolation of the climb speeds in the AOM table. Usually, it works out to about 1 KIAS/1000 feet. When you get to the slowest published number up in the 30s or .63 intercept (faster if bumpy), ensure that it remains in Mach until level-off. As you get to level-off and see ASEL on your scoreboard, flick the selector to FMS speeds so that it can accelerate to your cruise speed without throttling back first. Depending on the conditions, you will have just saved 100-400 lbs on your climb burn vs 280/.74. Due to your level-off occurring earlier, your cruise will be a bit longer, so some of the climb savings will go to a longer cruise segment, but you should be 100-200 lbs up from plan at your first post-ToC waypoint under most circumstances.
20/80 Technique
If you want to get 80% of the output for 20% of the work (e.g. short flight, briefing to do, lazy on last leg, etc.), just put 240/.65 in the box and let it do its thing. If it’s bumpy up high or you’re heavy, make the transition at .67-.70 or as appropriate for your cruise altitude.
Limitations
This technique is a great way to save fuel when you’re over-blocked, leaving a quiet outstation, or have the time to spend 1-2 mins on the climb. There are a handful of situations where you do not want to climb at best efficiency:
- Departing a busy Class B with traffic behind you: going slower than 270 is a great way to mess up spacing and annoy controllers. If everyone else is climbing at 270-310, you putzing around at 240 will gum up the works and likely waste more fuel at a system-wide level if others need to zigzag around you or slow down to maintain spacing. Don’t be that guy.
- You’re late: sometimes you need to go fast to preserve schedule integrity and connections.
- Turbulence: if it’s bumpy, give yourself more margin above green dot and pick it up if you see the eyebrows.
- Strong headwinds at altitude: it’s a bit tricky to model the benefit of improved climb efficiency versus the additional penalty of a stronger headwind aloft and how you net out, that might need to be the topic of another article.
What about galley carts?
I got a reader question about the steeper pitch angle and its effect on pushing a galley cart up the aisle. If we have a cart of weight W and a pitch angle, θ, then the longitudinal force L can be obtained through vector decomposition as L=sin(θ)*W. Using some sample θ values from a recent flight at 73,000 lbs climbing 240/.67 and assuming a 50 lb cart, the values for L are listed below:
|
|
Faster climb speeds usually result in θ values that are 1-3 degrees shallower in the 20s and up, where carts usually get pulled out. Eyeballing that table gives about a 1 lb load change per degree θ, in other words not a large difference.
Conclusion
Using the optimum climb speeds that Embraer provides will save you 100-200 lbs per segment, thus giving you more play fuel for holding, environmental savings, and cost savings. All you need to do is dredge up page 6-10 in the AOM Volume 1 and fly those speeds.