Types of aviation altitudes:
Indicated altitude is the reading on the altimeter when the altimeter is set to the local barometric pressure at Mean Sea Level.
Absolute altitude is the height of the aircraft above the terrain over which it is flying. Also referred to feet Above Ground Level (AGL).
True altitude is the elevation above mean sea level.
Height is the elevation above a ground reference point, commonly the terrain elevation.
Pressure altitude is the elevation above a standard datum air-pressure plane (typically, 1013.25 millibars or 29.92″ Hg and 15°C). Pressure altitude and indicated altitude are the same when the altimeter is set to 29.92″ Hg or 1013.25 millibars.
Density altitude is the altitude corrected for non-ISA (International Standard Atmosphere) atmospheric conditions.
Our aircrafts performance depends on density altitude, which is affected by barometric pressure, humidity and temperature. On a very hot day, density altitude at an airport (especially one at a high elevation) may be so high as to preclude takeoff, particularly for helicopters or a heavily loaded aircraft.
With that in mind, lets assume the nice warm weather we have witnessed over the last few days will affect our seaplanes performance capabilities!
Annual Inspection = √ Check! Registration = √ Check! Radio Permit = √ Check! Operating Limitations (POH) = √ Check! Weight & Balance= What? Performance Calculations = What? Maybe this is the perfect time to have a little sit down pow wow with a nice CFI or a fellow seaplane pilot or simply for spending some time with our POH and how density altitude may affect our next flight. On a day like today, in New England, with temperatures hitting 91 Fahrenheit and the winds rather calm we may find fairly calm waters and an awesome flying scenery, but we are also asking a lot from our airplanes performance capabilities. Taking the time to do a few simple W&B and Performance problems may give us some better level of awareness as to what may be expected. It also gives us added confidence to see how far from the MAX we actually are, on this flight. It also tells us exactly how many cooled beverages, fishing gear and other fun utensils we may pack for the fun in the sun, because we never want to hit stuff…