PLT285: Height Velocity Diagram
What code PLT285 covers, why the FAA tests it, and how to study Height Velocity Diagram before your checkride.
Recall information on a Height Velocity Diagram
What this means for your checkride
The height/velocity diagram depicts the combinations of altitude and airspeed from which a successful autorotation can be made after a power loss. The shaded area on the left marks profiles with too little airspeed to enter an autorotation in time, and the shaded area at the lower right is dangerous because low altitude and high speed leave too little reaction time. The diagram is valid only when the helicopter is operated within the gross weight versus density altitude chart, since weight and density altitude affect the altitude needed to reach a steady autorotative descent. The typical safe takeoff profile stays clear of these shaded areas by accelerating through translational lift before climbing.
Staying out of the height velocity shaded areas directly affects survivability if the engine fails, so pilots must interpret the diagram.
The diagram is not a regulatory restriction, and the lower right shaded area does not apply to multiengine helicopters able to fly on one engine.
Where to study it
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.