14 CFR 23.1303 - Flight and navigation instruments.
The following are the minimum required flight and navigation instruments:
(a) An airspeed indicator.
(b) An altimeter.
(c) A magnetic direction indicator.
(d) For reciprocating engine-powered airplanes of more than 6,000 pounds maximum weight and turbine engine powered airplanes, a free air temperature indicator or an air-temperature indicator which provides indications that are convertible to free-air.
(e) A speed warning device for -
(1) Turbine engine powered airplanes; and
The speed warning device must give effective aural warning (differing distinctively from aural warnings used for other purposes) to the pilots whenever the speed exceeds Vmo plus 6 knots or Mmo 0.01. The upper limit of the production tolerance for the warning device may not exceed the prescribed warning speed. The lower limit of the warning device must be set to minimize nuisance warning;
(f) When an attitude display is installed, the instrument design must not provide any means, accessible to the flightcrew, of adjusting the relative positions of the attitude reference symbol and the horizon line beyond that necessary for parallax correction.
(g) In addition, for commuter category airplanes:
(1) If airspeed limitations vary with altitude, the airspeed indicator must have a maximum allowable airspeed indicator showing the variation of VMO with altitude.
(2) The altimeter must be a sensitive type.
(i) Is powered from a source independent of the electrical generating system;
(ii) Continues reliable operation for a minimum of 30 minutes after total failure of the electrical generating system;
(iii) Operates independently of any other attitude indicating system;
(iv) Is operative without selection after total failure of the electrical generating system;
(vi) Is appropriately lighted during all phases of operation.