Your Static Ports Stay Open So what happens if your pitot tube ices over, but your static ports stay open? There are a couple different cases here, but let's stay the whole thing iced over, including the drains. If this happens, your ram pressure gets trapped. And just like the first scenario, if nothing changes, you're fine. But what happens if you start climbing? Your static pressure decreases, and the trapped static pressure component of your ram air is too great, which means you're indicating a faster speed than you're actually flying.
And if you descent, the exact opposite happens. If this happens, all of your ram air will leak out the drain, and you're left with nothing but static pressure. And if that happens, your airspeed goes to 0. If your entire pitot tube and static ports ice over, chances are you have bigger problems than just airspeed. But just so we've covered it, your airspeed indicator will freeze in place, because there will be no changes to static or ram pressure.
Keeping your ports clear is obviously important, and the best way to do that is with pitot heat when you're in icing conditions. But beyond that, it's critical that you make sure your ports aren't clogged with anything before you leave the ground. Become a better pilot. Subscribe to get the latest videos, articles, and quizzes that make you a smarter, safer pilot. Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ, and has directed development of numerous commercial and military training systems.
You can reach him at colin boldmethod. The ASI uses the aircraft pitot-static system to compare pitot and static pressure and thus determine forward speed. Airspeed is usually measured and indicated in knots nautical miles per hour although other units of measurement are sometimes encountered.
On older aircraft, airspeed is usually indicated to the pilot on a graduated scale over which a pointer moves left hand picture below. In modern aircraft, it is usually indicated on a speed tape which forms part of the Electronic Flight Instrument System display left hand side of right-hand picture below. Both can be fed from the same system in the event of failure of one system. A leaky static line can be hard to detect in an unpressurized aircraft , and may only be found during the biannual system check.
The fittings and tubes may have developed a small leak that could lead to inaccurate readings. The casing around the instrument or the fittings for the tubing could admit air, leading to inaccurate readings. A lower-than-normal indicated speed when the throttle is set for cruise RPMs may be the first sign of an air leak. If only the static port is blocked, the airspeed indicator will operate, but it will be inaccurate.
Depending on the altitude of the aircraft when the blockage occurred, the airspeed could read higher or lower than usual during flight due to static air trapped in the instrument case. All mechanical airspeeds have sealing gaskets, bezel gaskets and diaphragms. Any one of these parts can cause the airspeed to leak. Age, over pressuring the diaphragm and environment will cause gaskets to deteriorate over time. Because a blocked static port traps the static pressure at the density altitude of the blockage, indicated airspeeds will vary based on altitude.
If a plane with a blocked static port climbs, the Airspeed Indicator will read low, and if the plane descends, the Airspeed Indicator will read high. In addition to telling the pilot how fast the plane is going, it also shows, via colored arcs, different operating speeds depending on configuration.
An Airspeed Indicator operates using a pressure differential, taking a static pressure reading from the static port, and a dynamic pressure reading from the pitot tube. Knowing and understanding how an Airspeed Indicator reads during a blockage is critical for safety. Your email address will not be published.
Notify me of follow-up comments by email. Notify me of new posts by email. Home Aircraft Airspeed Indicator Explained. There are only a few non-engine indicators that an airplane really needs for VFR flight. If you go too slow, the plane will stall, but if you go too fast, you risk structural failure. What is an Airspeed Indicator? Related Article — Aircraft Altimeters Explained 2.
How does an Airspeed Indicator work? It is the one instrument which uses both the pitot tube and static port in conjunction. Airspeed Indicator Colors Explained On the face of the Airspeed Indicator are several colored arcs, white, green, yellow, and a single red line.
See the diagram below for the bigger picture. Airspeed indicator markings.
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