boy could i write a long one on this subject. most of my 60 signoff's have been for instrument ratings, not counting training captain time and work as a lear check airman..basically an instrument ride in the jet.
i spend several hours of ground with a beginning instrument student on understanding the flight instruments, how they're powered, the primary and supporting method, various scans patterns to include the 'inverted v' scan to quickly catch a failure in either the pitot/static, electric or vacuum systems. i go into depth to explain from the primary/supporting method, of how in every single phase of flight, you have one primary pitch and one primary bank instrument, and that all the others are supporting these.
part of the utility in this is that when it's night..and you're in the soup, and it's raining and lightning and turbulent..you have your hands full as a single-pilot ifr pilot. single pilot ifr is much more challenging than crew flight, where one has the luxury of a co-pilot to assist in working radios, tuning frequencies, running checklists, etc.
the most simple example of a phase of flight is simple straight and level. you have several flight instruments that provide pitch information: airspeed, attitude indicator, altimeter and vsi. but only ONE can tell you that your pitch is level and that you're at the ASSIGNED ALTITUDE - the altimeter. same for bank..you have the attitude indicator again (also the only one that gives you 'pitch and bank at a glance', your 'window to the outside in imc' and your 'workload management instrument'), the heading indicator and the turn coordinator. all three will give information that your wings are level, but only one will show you on the ASSIGNED HEADING - the heading indicator. so..in the soup, with your hands full, and your task is maintaining straight and level flight, you have just two instruments you have been trained to concentrate more attention on, rather than six, to stay straight and level.
level turn? altimeter and turn coordinator. descending constant-rate turn? turn coordinator and vsi. constant airspeed climb? airspeed indicator and turn coordinator. level constant airspeed climb? airspeed indicator and heading indicator. how about a vor approach? heading indicator and vsi. the vor head is a supporting instrument. only ONE wind-corrected heading will maintain the course and you're targeting a rate descent to get to your mda. i have my students write up every possible phase of flight and have them draw a simple diagram of which instruments are primary and which support. no matter what, i automatically know which two instruments are giving me the most pertinent information for that flight phase.
workload. what's that? anythinf that takes your attention in imc away from the primary flight instruments (six pack) for more than 2-3 seconds. this can mean tuning a radio, checking an engine instrument, looking at a chart, picking a chart up off the floor, setting power, etc. i teach that the last instrument they check before leaving the 'six pack' is the attitude indicator and for each 2-3 seconds they're away, to simply glance up at it to maintain control. more than likely, you'll stay within tolerances. once the task is accomplished, return to the six pack via the attitude indicator, return to the primary two instruments and check for deviation.
deviation? the attitude indicator is ALWAYS primary whenever transitioning between phases of flight, say from straight and level to a climb (put the miniature airplane into an approximate climb and then transition to a constant airspeed climb where the airspeed and heading indicator are now primary). back to deviation: if there is a deviation after the task, go to the attitude indicator to correct the deviation. once corrected, return to your two primary instruments for pitch and bank.
more on the 'inverted v' scan..it's very important. the inverted v is the attitude indicator, vsi and turn coordinator. here's the check: the right side of the v..the vsi and attitude indicator. simply put the aircraft into a small climb or descent. there should be agreement between the two instruments. if not, IMMEDIATELY check the suction gauge. you may have a vacuum failure. it's easily caught on the suction gauge. same for bank, the left side of the 'v'. put the aircraft into a simple bank. if disagreement between the attitude indicator and turn coordinator, IMMEDIATELY check the suction gauge again. if you have suction, you've lost the t.c. if you don't, you've lost vacuum, which means both attitude indicator and heading indicator.
the thing with losing vacuum is that the gyros are spinning at some 18k rpm. they spin down slowly. this means the attitude indicator will begin to slowly start indicating a roll in one direction, although it isn't real. you'll compensate, by turning in the opposite direction. eventually, you'll become inverted, your airspeed will be increasing rapidly, you'll wonder what's going on and quickly become a statistic. keep a close watch on your suction gauge and make the inverted v a regular part of your scan.
i also teach a routing flight instrument check during taxi. it's a circle scan. we start in the upper right hand: "airspeed indicates zero" (it should), "wings level" (set it with knob), altimeter set to ___ or field elevation", "vsi indicates zero" (or note error for level flight), "i have ____ degrees once" (read from compass), "twice" (set the H.I. to the compass), "right brake, left ball, left brake right ball" (checks ball) and turn indicator correct", "flight instruments checked". next engine instruments (trainer aircraft) "oil pressure in the green, oil temperature rising and ammeter indicates zero (neutral)" or "charging". "taxi checklist is complete".
at any rate, that's a sample of things i've learned to emphasize, both from thousands of hours instructing and thousands flying freight, charter and int'l air ambo in the system. hope someone might find it helpful. i no longer fly professionally, but returned to general aviation to have a home life, instruct for a profession..and because i find i'm patient and enjoy teaching. ymmv. :bandit:
there's certainly more than one way to 'skin a cat' and great pilots come from a variety of different training methods. the faa likes the primary/supporting method. i like to think they generally know their business..we're simply their ambassadors. :bandit: