@UNCTUOUS
What is your mechanism for a pitot to slightly under-read?
If the ram-port blocked the the indicated flow will fall to zero if the drain open - guess you are looking for partial blockage of ram with drain open? If the drain also blocked the total pressure locked and indicated flow will vary with static pressure (known danger during take-off climb). I fear drain holes blocking at similar rate on more than one pitot could lead to small over-read before all 3 disagree, but as Takata has already pointed out still unlikely.
What are the real speed margins before or after a reduction in speed for turbulence entry?, and what is magnitude of drain hole blockage effect? If ice detected/suspected how much engine power will be used on wing anti-icing measures?
@
auv-ee
Its going to be very difficult to maintain the temperature of pitot tube in 500 mph wind at much above the ambient air temperature - monitoring the power needed would turn it into a "hot-wire anemometer". If melting out ice the surface in contact with the ice will be at the freezing point of the water - a principle you could use to detect ice! You do need temperature control when on the ground to avoid turning the probes into soldering irons.