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Flight instruments provide the pilot with information about the flight situation of that aircraft, such as altitude, speed and direction; and are of particular use in conditions of poor visibility, such as in clouds, when such information is not available from visual reference outside the aircraft.

48 votes
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Why do digital flight instruments seem to fluctuate/flicker during landing or takeoff?

In short: The reason you see this is two-fold: Usual CRT flicker by principle, CRT frames are not displayed in their entirety at any time, but this is not visible to the naked eye, due to the frequen …
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6 votes
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What is gimbal error in DGI compass gyroscopes?

Short answer The gimballing error is the mechanical error introduced by the cardan design of a gyro DI. A cardan joint is linear only when its input and output axes are aligned. In the gyro DI axes ar …
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13 votes

What is the purpose of the leaf spring in an altimeter?

Without the spring, the capsule would tend to collapse at or below sea-level pressure-altitude. The spring opposes the high pressure. Source A variation of the principle above it to put the spring on …
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3 votes
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What will the pilot do if all the airspeed indicators fail?

Are there any alternate instruments to indicate the airspeed From SKYbrary: Reliable Sources of Information The following information sources, independent of the pitot static systems, …
1 vote

Does the glide slope flag detect percent of modulation (80%)?

I wanted to post this as a comment, but it's a bit long. From ICAO Chicago Convention annex 10, vol 1: 2.3 Alarm conditions for ILS airborne equipment 2.3.1 Ideally, a receiver alarm system such as a …
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5 votes
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Can you fly with INS/ IRS at higher lattitudes?

Yes this would be possible. The limitation is for gyro-compassing only (alignment). However being technically possible is only one aspect, there are associated regulations. Going into polar regions is …
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4 votes
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Does the infinite focal point in a HUD resulting from the collimation mean the HUD is ALWAYS...

The projector and the combiner create a virtual image on the other side of the combiner mirror. This image is perceived like a true image. The eyes need to adapt the focal length to the distance of th …
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7 votes

What type of altimeter is this?

It seems to be a C-12 or C-13 sensitive altimeter (SA) from Kollsman Instrument Division / Square D Company, manufactured circa 1940: (Source) The only difference seems to be the marking "ALTITUDE" …
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6 votes

How did planes measure their speed relative to the ground before GPS?

How did planes measure their speed relative to the ground before GPS? Assuming you ask for speed determination by on-board instruments. The ground speed is best evaluated using an inertial nav …
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13 votes
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Were the original gyroscopic artificial horizons "upside-down"?

Yes top and bottom were reversed, and there were labels to indicate climb and dive directions. Sperry advertisement circa 1959: Source However such indicators were competing with another design from …
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20 votes

What kinds of altimeter are used in modern airliners?

Main instruments In large aircraft, main altimeters are not separate mechanical altimeters. Instead the pitots, static probes and angle of attack probes, which are redundant, have their outputs digita …
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3 votes

Anybody recognise the model of ADI on the XB-70?

The Mirage III had this kind of spherical indicator, combining attitude and heading indicators, known as Bezu ball, after its inventor: Source. So it is truly a complete sphere? Yes. Source. In w …
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5 votes
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How can I switch from MAG to TRU heading in a 737?

This switch is part of the Heading Reference System available only for customers who bought the Polar Operations option. As the PDMG 737 MAX add-on is not yet available I assume this is for the 737 NG …
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12 votes

What is the correct crew procedure for an unreliable airspeed alert?

As you probably know this is the situation that occurred for AF-447 (Rio-Paris) on June 2009. From the BEA report: The accident resulted from the following succession of events: Temporary inconsiste …
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29 votes

What is that missing instrument on a Beechcraft 1900C?

Originally there was no instrument at this place, except for UE series with an electrically driven artificial horizon, where there was a fast erect pushbutton/indicator for the copilot gyro. Accordin …
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