I have been using VNAV a lot recently for descents and sometimes it’ll descend me at -3000fpm and it’s really annoying. Any solutions?
Try to either type in your own altitudes for your VNAV to descend to. Therefore, you can control the rate a lot easier. Or, you could turn the VNAV on once you hit cruising altitude. I do that, and I get at most -1200 fpm, but I usually get -600 fpm. That’s just what I do, so you don’t have to follow what I say.
Your VNAV will always descend at a rate necessary (not to exceed 3000fpm) to meet the various altitude assignments throughout your descent. These are often automatically populated into your flight plan if descending via a STAR, though you can manually change them yourself if you want control how aggressive or conservative you’d like the various altitude intervals to be.
Check out my Descent Tutorial to learn the ins and outs of VNAV:
Are you only using VNAV on the STARs?
And thus is the skill involved in instrument flying, ensuring you don’t find yourself in a situation like this.
It’s not particularly difficult but a bit of math helps you visualize ahead of time what you’re looking at. Altitude to lose over distance to run will give you the descent rate required, although since we are working with distances that descent rate is in feet per nautical mile rather than feet per minute.
A faster airspeed will require faster descents in feet per minute to achieve the same feet per NM descent angle, since you are covering more ground in the same amount of time. So slowing down will help make the steep descents more manageable, but you will still find yourself looking at fixes and realizing its not possible to descend that fast in such a short distance, and you’ll need to adjust accordingly.
This is partly because IF is not able to read charted altitudes well, it can’t determine if something is an altitude restriction, an at or above limit, or an at or below limit. So first step is to pull up the chart and verify the altitudes are correct, 75% of the time they won’t be and need to be changed.
Even so, it may still be difficult and you will have to decide what to do especially when flying slippery planes like the 777. If you are descending too fast on VNAV and starting to accelerate, you have a choice: you can turn off VNAV, reduce the descent rate and get your airspeed under control, but this means you won’t hit your altitude restrictions. Or, you could continue to descend, allow your airspeed to increase, and then slow down once you level off. If you’re below 10,000 feet, this might not always be an option. But regardless, you have to choose what’s best given the context.
that explains why i have like -2500fpm on descent via STAR. cause i bomb it in at cruise speed lol