I was on the Salty discord and some guys were talking about landing speeds, so I did this little blurb about how to calculate speeds. I thought some others may benefit from this too. Feel free to ask questions if this doesn’t make sense. This was for the 747, but works in all Boeing, CRJ, and Embraer, as far as I’m aware.
For those interested in calculating landing and approach speeds here’s how it goes:
There are a couple of conditions to be aware of; Steady State Headwind Component and Gust Factor. For this example, we’ll use runway 36, and our VREF is 155 knots for our weight.
With a VREF of 155, you’d fly the approach at 160 (VREF+5) for a 0-10 knot headwind. When you actually touch down, your speed should be at VREF, you bleed off the steady state headwind additive for the actual landing. The MAXIMUM you’d add is 25 knots over VREF, this includes steady state headwind AND gust. NOTE: You’ll never fly an approach at VREF, it’ll be VREF+(a minimum of) 5 knots.
- Let’s start with the Steady State Headwind Component. You’ll always approach with VREF+5 in a low wind condition (between 0 and 10 knots of headwind), but, your touchdown should be at or around VREF…in other words, you’ll bleed off the steady state headwind calculation.
1a) To calculate the steady state headwind component, you take half of whatever the headwind is, and add it to your VREF, but, remember, you’ll always approach with an additive of 5 regardless of the headwind, up to 10 knots. This can be a little confusing to see at first, let’s take a look at a few examples, so you can see what I mean.
1b) Landing runway 36, the winds are 360/8, giving us a steady state headwind component of 8 knots. In this example, if we take half of the steady state headwind component, 8, we get 4. That would mean, our VREF would be 159 (155+4), but remember, we have a minimum to add of 5, which means…our VREF is 160.
1c) Here’s another one. Landing runway 36, the winds are 360/14. This gives us a steady state headwind component of 14, so our additive is…you guessed it, 7. So, we add that 7 to our VREF of 155, and that comes out to be an approach speed of 162.
1d) Here’s another example. Landing runway 36, the winds are 270/35 (direct crosswind). Since there is no Steady State Headwind Component, you’ll approach with…VREF+5, which is 160.
On to Gust Factor
- The gust factor is the difference between the steady state wind (not the steady state headwind) and the gust. In this condition, you actually DO land with the gust additive, as opposed to bleeding it off, like you would with the Steady State Headwind Component.
This is where it gets a bit confusing, but I’ll try my best.
When you add a gust factor, you get rid of the 5 knot minimum additive (VREF+5). This prevents you from adding everything on top of 5 knots. In other words, the gust additive overrides the 5 knot additive, VREF is our Base.
The conditions remain the same as above: runway 36, and our VREF is 155 knots for our weight.
2a) Landing runway 36, the winds are 270/7G20 (direct crosswind). The difference between 7 (the steady state wind) and 20 (the gust) is …13. So in this scenario, you’ll approach and touchdown with 13 knots of protection, giving you an approach speed of (155+13) 168, and landing a landing speed of 168 knots. NOTE: It’s not VREF+5+13. It’s VREF+13.
2b) Here’s another one. Landing runway 36, the winds are 360/10G15. The difference between 10 and 15 is 5. This adds a bit of complexity because we have a Steady State Headwind, AS WELL as a Gust Factor. Let’s break it into two-ish parts.
-First, The Steady State Headwind: Well, half of 10 is 5…we’re going to add the minimum of 5 over VREF which gives us 160.
-Next, we have to add the Gust Factor. The difference between 10 and 15 is 5, so we add that to VREF giving us, 165.
-So here comes the fun part, what speed to we approach with, and what speed do we land with? The approach is flown at 165 (VREF+5+5). We land with…160 knots, because we bleed off the Steady State Headwind Component, but land with the Gust Factor.
2c) Last example. Landing runway 36, the winds are 360/15G40. Half of the steady state headwind is 7.5, but let’s round up and call it 8. So we’re currently at VREF+8. Now we have to add the Gust Factor. The difference between 15 and 40 is 25. So we add, VREF+8+25 (155+8+25) which gives us 188…But remember, the maximum we add is 25 knots total. So our VREF would be 180. But what do we land with? Well, we still bleed off the Steady State Headwind, so our touchdown would be 172 (180-8). <—That could be argued.
For landings with winds that aren’t directly down the runway, the link below can be used to determine your steady state headwind component.
I hope this helps a bit, feel free to ask questions if you need help understanding this.
Just remember, everything is added to VREF. VREF is our base for the calculation. You’re always going to approach with a minimum of VREF+5.
Here are some problems for you to solve. What’s your VREF? Same conditions as above:
Runway 36, VREF of 155
A) Wind 360/12
B) Wind 310/6G18
C) Wind 180/10
D) Wind 330/11G20