Are there any alternate instruments to indicate the airspeed in case of pitot tube failures?
Are there any alternate instruments to indicate the airspeed
Reliable Sources of Information
The following information sources, independent of the pitot static systems, can provide reliable information for situational awareness:
rpm, and fuel flow, for engine thrust indication (not EPR, which may be unreliable);
Pitch and bank display;
FPV (Flight Path Vector) if available and derived from inertial and not barometric sources;
Radio height when below 2500ft agl;
Stick Shaker - may not always be activated but if it is, it is independently reliable;
Navigation systems can provide ground speed and position information (GPS can also provide altitude information);
Radio navigation aids and RNAV.
ATC, in a radar or ADS-B environment, can provide aircraft ground speed.
If TAS can be determined, a rough approximation of IAS at altitude can be calculated by the fomula: IAS=TAS – (FL÷2) eg 400TAS FL300 = 250IAS.
Note: Some aircraft systems are configured, as a safety measure, such that stick shakers and pushers will not operate if there is disagreement between systems. Thus, if the aircraft approaches and/or enters a stall, these safety features might not activate. However, if the stick shaker does activate, it should, in the absence of clear contrary indications, be believed.
Some aircraft have angle of attack indicator, but most don't even though they have the sensor and use it for stall warning.
What you normally have is an unreliable airspeed procedure. This generally says that you should, depending on phase of flight, maintain specific pitch, set specified thrust and then adjust for rate of climb/descent while keeping the pitch.
Since aircraft is trimmed for speed, generally the procedure calls for being light on controls and correct mainly with engines. Exception is Airbus which keeps auto-trimming even with speed disagree warning on, so there side-stick controls climb and power controls pitch almost independently.
See also unreliable airspeed procedure for A330.
Depends of the type of aircraft - does it have a secondary pitot, inertial nav etc. If it does - you're in luck. Also - "Pitot failure" - that would mostly be clogged total pressure tube (insects . . . .), but could also be static, in which case pressure altitude & rate of climb may be unreliable too. In other words - have to watch for overall funny behavior.
An alternative is getting ATC involved. They could give an estimated speed of the aircraft. Since speed is distance travelled over time, ATC should be able to take the time difference between the two blips on the radar. Knowing the scale of the map in the radar, they can work out your speed.
If the radar has a scale of 1km represent 1cm on the radar screen, and the blip refreshes every 4 seconds. ATC could measure with a ruler (on the radar screen) the distance between the previous blip to the new blip, say this is 1cm. You know that 1 cm is actually 1 km in real life, and the the time between blips is 4 secs. So the plane has travelled 1km in 4 seconds which is about 250m per second (1000m / 4seconds). 250 m/s equals to about 900 kph. The ATC could give you updates on your speed.