AIRNAV   (Warning:- Not to be used for real world aerial navigation!) 
 
Airnav is a Psion 3a Spreadsheet which is a simple introduction to some of 
the calculations used in flight planning and navigation. Airnav is intended 
for use only in conjunction with computer flight simulators such as 
Sub Logic's Air Transport Pilot (ATP) or Microsoft Flight Simulators 4&5 
(FS4 & FS5) or any other "realistic" flight simulator.
The calculations are oversimplified should not be used for real world aerial 
navigation. 
 
The data entry required is in cells B1 to B8 and is shown in bold type.  
Units used are shown in column C. 

The following calculations are performed: 
 
INDICATED AIRSPEED (IAS) TO TRUE AIRSPEED (TAS) 
Input: IAS , altitude ( above sea level) - cells B1, B2 
Output: TAS (knots) - cell B10 
Comments: 
The aircraft's air speed indicator does not read true airspeed at higher 
altitudes due to the lower air pressure. In the spreadsheet a simple
correction factor is applied from a look-up table (cells E1:F14). 
 
WIND CORRECTION FACTOR TO SPEED 
Input: As above (IAS, ALT) +Course, Wind direction, Windspeed 
Output: Speed corrections:TAS, Groundspeed, Headwind, Sidewind(or Crosswind) 
Comments:  
Course is the desired  track over the ground.  
All directions are compass headings in degrees (magnetic)  

WIND CORRECTION FACTOR TO COURSE/HEADING 
Input: As above (IAS, ALT ,Course, Wind direction, Windspeed) 
Output: Course corrections: Wind correction, Heading 
Comments:  
Course is the desired  track over the ground.  
Heading is the compass heading on which the aircraft must be flown in order 
to fly the desired track after allowing for being blown off course by a
sidewind. If sidewind is zero then course and heading are the same. 
All directions are compass headings in degrees (magnetic) 
Headwinds have negative values. A positive value indicates a tailwind. 
Wind correction is negative for westerly and positive for easterly winds. 
 
APPROACH & DESCENT CALCULATIONS 
Input: As above + Field Altitude & distance(DME) 
Output: Glideslope, Rate of Descent(ROD), Estimated Time of Arrival(ETA) 
Comments: 
This calculation helps you plan that all important descent and approach to the 
runway. 

Field altitude is the height of the destination runway (above sea level) 
taken from the airport chart (Note: if you are not landing but just descending 
to a new altitude, eg to get below a cloud base, just enter the final altitude 
required) 

Distance (DME): Distance measuring equipment (DME) provides the pilot with 
a panel readout of the aircraft's distance from a selected VOR station, 
in nautical miles. Tune the NAV radio to a VOR station at or near the    
destination airfield and enter the DME distance reading.

Glideslope: As a guide the glideslope used in civil aviation is 3.5 degrees 
which makes for a comfortable landing. If your calculated glideslope is very 
much greater than this then you are either landing on the deck of an aircraft 
carrier or flying for "White Knuckle Airlines". 

Rate of descent (ROD): In FS4/5 it is useful to be able to configure your 
Cessna aircraft for landings with an airspeed of 80-90 Knots (IAS) and 
rate of descent of 500 fpm. 

ETA: Try using a stopwatch to time your descent at constant speed & ROD 
particularly if you are making an instrument approach through cloud or fog. 
Using the above speeds you will be 500ft above the field and 1.5 nm from the 
runway threshold 1 minute before the calculated ETA.  
If you have the runway in sight and are reasonably aligned for a landing, 
- go for it. If not, it might be prudent to increase the power for a climb 
and call a missed approach. After all a good pilot is one who makes as many 
landings as he does take-offs! 
 
This spreadsheet is freely available for use by members of 3-Lib. 
The author accepts no liability whatsoever for any errors, damage or losses 
arising from its use. 
 
John Swash,  
May 1995 
 
Footnote: 
Flight Simulator User Group, FSUG, is a club for people with a general interest 
in aviation & flight simulators in particular. It has 300+ members; quite a 
few are private pilots or have other expertise eg gliding, ex-RAF or Air 
Traffic Control.  
Annual membership is 10 pounds for which you receive a bi-monthly newsletter.
Interested? -Contact Phillip Pattinson, FSUG Membership Secretary,
28 The Drive, Hipperholme, Halifax, HX3 8NT. Tel: 01422 205415 (after 6pm).