Pitch and power are great tools, whether you've got a good IAS indication or not - belt and braces? But although the pitch values are easily remembered (remember the mnemonic "(DTD)585" for the B707?), the N1 or EPR settings are less so, unless you have noted the setting just before the IAS indications go AWOL. It can take a while to find the appropriate page in the QRH. On some a/c, the total fuel flow is a better tool than N1 or EPR, but it's not generally taught, and digital flowmeters don't seem to be as user-friendly as the old analogue ones.
I have a pipe dream in which the TAS would be detected by a kind of anemometer mounted at a suitable point on the fuselage. Provided the static pressure and TAT were available, the ADC could then calculate the CAS/IAS, and of course the Mach. But an anemometer might be even more prone to icing than a pitot head, and its RPM could be problematic...
Quote from glendalegoon:
Talking about radar, wondering how many people remember Doppler Radar Nav which gave us ground speed/drift? I only knew about it because all of our planes of a certain age had the sticker: DOP INOP
Suspect you may be betraying your age as sixty-plus?
Most Doppler-equipped a/c must have been retrofitted with INS by the late 1970s. IIRC, our B707s had their Doppler removed at the same time. As you no doubt remember, it wasn't much good over smooth sand or calm sea.