Thursday, September 30, 2010

Flying On Instruments-Part 1

This is the first in a series telling “all” about flying on instruments. I have written about flying IFR (instrument flight rules), and decision making etc., but not led you through all the nitty gritty. This first part will deal with the basic instruments and radios used.

Regardless of the type of IFR weather, there are certain basics that will always apply. Some of these conditions also must be followed in VFR flight as well. In order to achieve flight, a certain airspeed, as shown on the air speed indicator must be attained. Things that affect necessary air speeds include: temperature, aircraft weight, and flight conditions such as: turbulence, ice etc. Failure to achieve or maintain necessary
speeds may mean inadvertent stall e.g.(recent case in Buffalo). If certain speeds are exceeded however, as in an uncontrolled dive, the plane may disintegrate in mid-air. This maximum safe speed (VNE), is indicated on the air speed indicator with a red line. Prior to that there is a caution zone outlined in yellow. The safe zone is “in the green”.

The airplane attitude (position relative to the horizontal) must be kept within certain reasonable limits. This is done with the aid of info from the artificial horizon, perhaps the most important gage of the instrument flight array. This instrument gives a pictorial image of the plane’s flight with respect to bank angle and pitch (climb or descent). Turns generally shouldn’t involve more than a 30 degree bank angle. Recently a tragic crash occurred near Charlotte with bank angles achieved greater than 60 degrees. These are ok during certain maneuvers but never during instrument flight. Severe bank angles markedly increase stall speeds that may lead to disaster. Similarly, climb and descent angles are limited to relatively small values. All is done in order to maintain positive, safe control of the airplane. Problems arise when for what ever reason, a pilot gets distracted, or is too busy to keep things within safe parameters. Accidents sometimes occur for example, when an inexperienced pilot suddenly encounters instrument conditions (loss of visual cues).

The final primary instrument I will discuss is the easiest to understand, the altimeter. It is nothing more than a barometer calibrated in feet or meters. Usually it can indicate differences of 20 feet and goes from below sea level (flying in a gorge out west) to many thousands of feet. Flying either VFR or IFR generally requires adhering to certain rules that specify what altitude may be flown. In controlled airspace, as for example round major airports definite altitudes will be assigned by controllers (ATC). Almost all IFR flights are conducted under direct ATC oversight, and will entail flying an assigned altitude. Failure to adhere to this altitude may be the set up for a collision, or at least the cause for a collision alert system to activate if present on the plane. All US airliners have these systems aboard.

Finally, a functioning VHF (very high frequency) aircraft radio, preferably two or more must be aboard, enabling the pilot to communicate with ATC. Navigation radios are necessary and are frequently part of the communication radios. Several different types are needed and will be discussed later. Also a transponder is required which allows ATC to positively identify the aircraft position and altitude (mode c). ATC assigns a specific code (four numbers) to each flight.

That’s enough to get started on. I’ll discuss the pilot’s interaction with the above in a subsequent article about a real flight.