Density Altitude is Pressure Altitude corrected for temperature. It’s going to give you a good idea of what to expect from your helicopter. The warmer the air the less dense that air is, which means less bite for your blades and less oomph from your engine. Provided you plan well it’s not going to give you any issues but skip that planning or neglect it once your airborne and you could find yourself in trouble.
Manifold Pressure Jet Ranger Torque Temp Guage Astar Astar Torque
Lets say you’ve got a job on a beautiful Spring morning. Your going to be flying a crew around to inspect and repair well-sites. It’s going to take the best part of a day so you’ve got plenty of gas, the crew, their tools, you, survival kit, first aid kit, water and of course don’t forget your lunch. Your heavy!
You pick up from the airport and notice your helicopter has plenty of power to spare and blast off towards your first well site. You got the coordinates last night but couldn’t find your map so just dumped them in the GPS to save time (and besides it was wing night anyway), not realizing this left the highest well-site just after your fuel stop in the middle of the day. Not a problem you think, we had plenty of power with this weight at the airport. The problem is it’s now nearly 20 degrees warmer than this morning.
Have a look at your density altitude chart in you Aircraft flight manual. Lets say when you left the airport at 4000 ft and 5° C. You get to your site at 5000 Ft but the temperature is now 20° C. That’s a difference in density altitude of around 2000 ft. A significant difference and certainly enough to cause you some trouble if you haven’t given it any consideration. What could this lead too? More than likely you’ll find yourself settling with power.
As a quick refresher settling with power is not having enough power to arrest or stop your descent. Remember those four H’s?
Hot High Heavy Humid
As you can see in our scenario we are dealing with 3 out of 4 of those H’s. If you come in fast and steep your likely to find yourself with a higher rate of descent than usual but not wanting to disappoint your customers you keep on going not realizing your already at
So what can you do to avoid these situations? PLAN, PLAN, PLAN! and start the night before you intend to fly. GPS is an incredible tool but they don’t always give you the big picture. Dig out your map from the bottom of your helmet bag and plan your day.
- What's the best route considering the elevations and your weight?
- What is the temperature forecast to be?
- Did you check your performance charts to see if you can hover at your destination?
- How much fuel will you burn before you get there? Is it enough to allow you to hover there?
- Can you start at sites further away and then back track to reach a usable weight?
- Do you need to make two trips?
- If you are power limited how are you going to approach?
- A controlled, shallow approach will require less power but is the site big enough to allow this?