Expert: D. Norkus - 7/9/2009

Question
QUESTION: The arrangement of instruments in many general aviation light aircraft seems haphazard. Do you agree? Isn't it better to have the engine RPM gauge close to the basic six instruments?
What is the scanning pattern and frequency of scanning the instruments during an IFR flight?





ANSWER: Depending on what you are flying, instrument or gauge modifications or upgrades can result in a very haphazard display. Also, if it is an older aircraft, it may not even have a standardized display lay out.

In the GA aircraft I flew, most of the time the RPM gauge was close to the primary instruments. However, presentation all depends on the aircraft you are flying and what has been installed in a given location. Since RPM isn't on every scan, in my opinion it isn't critical if it is not adjacent to the basic six instruments.
The standard instrument presentation layout is considered to be:

These across the top row
Altimeter - Attitude Indicator - Airspeed

These three across the bottom row
Turn Coordinator - Compass - VSI

The traditional instrument scan is an inverted "V":

*Turn coordinator - Does it indicate level flight or a bank?

*Attitude indicator Does it show level flight or a climb/descent?

*Vertical Speed Indicator- Does it show an upward or downward trend?

I was taught this scan should only take about 5 or 6 seconds. You also cross reference your engine instruments from time to time.
This is just for straight and level instrument flying.

Secondary checks include:

*Airspeed- Constant for level flight (with speed loss or gain at a set power, you are not level. Check.)

*Compass Constant heading (Are you steady or turning? Check.)

*Altimeter for level flight (Are you climbing, descending or in level flight? Check.)

This page has some good instrument scan illustrations for different regimes of flight-
http://www.scribd.com/doc/3997215/Instrument-Scan-Study-Guide

This is especially handy for learning to cross check instruments for maneuvering during instrument approaches or departures.


Hope this helps,

Dottie






---------- FOLLOW-UP ----------

QUESTION: Thanks Dottie, that's very useful.

Do you find that instrument panels and for that matter engine cowlings should be about 6 inches lower to give better visibility over the nose? Do you find dual - needle altimeters difficult to read without making errors and  are the glass displays of modern GA aircraft more difficult to read, especially airpseed? I also find it confusing and annoying to have altitude in thousands of feet like FL 125 insted of 12,500 or 5,000 - why can't they put in a comma? For experienced pilots it may be ok but the readability is bad for new pilots and ordinary people.  

Answer
"Do you find that instrument panels and for that matter engine cowlings should be about 6 inches lower to give better visibility over the nose?"

Since I am very short, that would have been helpful! However I learned to make due with a very comfy portable cushion to fix that problem. Once I moved up to light twins like the Piper Aztec, I found that most had excellent seat adjustments and visibility for petite pilots was much better compared to the Piper and Cessna singles.

"Do you find dual - needle altimeters difficult to read without making errors and are the glass displays of modern GA aircraft more difficult to read, especially airspeed?"

Since I learned on the standard two hand 'steam gauge' altimeter, I never really though of them as difficult to read. That's just all I had, so I suppose I figured it out. I have not had the luxury of being able to fly a glass cockpit GA aircraft but don't think it can be that difficult once you get used to it. I flew over 5,000 hours on 'steam gauges' and found the transition to all glass challenging at first. The jet I fly now is all glass and once I got used to them, I found the altitude and airspeed 'tape' displays easier to read. In fact, they make scanning easier too as they are closer and border the sides of the attitude indicator display.

"I also find it confusing and annoying to have altitude in thousands of feet like FL 125 instead of 12,500 or 5,000 - why can't they put in a comma?"

The flight levels begin above 18,000ft (in the USA anyway), so anything under that should have a comma or be spoken as "One Two Thousand Five Hundred". Perhaps it is different in your part of the world. (As a domestic pilot, I can't comment on that.) Above 18,000 feet it called what it is- a flight level. Hence the 'FL350' or Flight Level Three Five Zero" is proper nomenclature.

Regards,
Dottie