SUPPLEMENTAL AND EMERGENCY PROCEDURES
Knowledge of GS is essential to you as a NAV/NFO. Knowing your GS will enable accurate
determination of ETAs and facilitate fuel planning. Comparing true airspeed and GS gives you
wind information. All methods of determining GS are similar in that they measure the amount of
time required to cover a known distance or determine the distance traveled in a known amount of
time. In order to perform a GS check you must:
Be tracking on a radial.
At cruising altitude in unaccelerated flight (at the calculated IAS for 240 or 270 TAS).
3. DME must be larger than your altitude in thousand-foot intervals. Example, if you're
flying at 12,000 feet, you cannot perform a GS check until past 12 DME.
Note the elapsed timer and note DME. After 1 minute of elapsed time, note DME and determine
distance flown. This will be speed in miles/minute. Inform the IP of your miles/minute speed.
To get miles/hour, multiply this distance by 60. The result is GS in KIAS. More accurate GS
checks can be obtained by timing periods greater than one minute.
At 210 KIAS IAS (at low altitudes) you are traveling at
approximately 3.5 miles per minute (every 0.1 NM equates to 6
KIAS with no wind). This fact allows you to make reasonably
accurate ETAs until the refined procedures above can be
Example: A 3.7 GS = 222 knots GS (3.7 multiplied by 60).
Most air route traffic control centers will be able to provide a GS readout if you are in radar
contact. This information can be used to check your own calculations.
This involves determining the magnitude and direction of the winds. There are always 2
components to the wind: crosswind and head or tailwind.
1. Crosswind. In order to determine the crosswind, compare your desired course/radial to
your heading. This is your crab angle.
Crab angle x GS (miles/minute) = crosswind component.
SUPPLEMENTAL AND EMERGENCY PROCEDURES D-1