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Radar Altimeter Failure

Today we did a trip from COS to ORD. COMPLETELY uneventful, except the last five minutes. Here is the deal, we were being vectored to the right downwind by ATC…everything normal and we are being set up for runway 22R until our radar altimeter (RA) went completely whacko!

But, before I explain what happened, let me talk about what the RA is and how it come into being in airplanes.

After many deadly accidents because of controlled flight into terrain (CFIT), that is where the airplane, without any mechanical problems is flown into terrain by the pilot(s) which is a result of losing situation awareness, specifically, not knowing where your airplane is in flight. Therefore, the FAA mandated that radar altimeters (RA) were to be put into all commercial, air carrier airplanes and maybe some non-commercial airplanes. What this does, is when the airplane gets close to the ground, the radar bounces a signal off the ground and the RA starts reporting the distance, in feet, above the ground as a numerical readout on your primary flight display (PFD) screen. 

On the CRJ, at 2,500 feet above ground level (agl), you start to get this numerical readout. This readout continues to the ground. Further enhancements though, include verbal callouts such as “500,” then from 50′ to 10′ at 10′ increments and a yellow ground reference bar, which references the ground, below the digital readout numbers of feet above the ground. If the airplane gets too low or is descending too quickly there are other aural indicators to warn you that something is not right. These situational awareness tools have dramatically decreased the number of flights of CFIT…though not totally eliminating them. Anyway, with this in mind, here is what happened during the last five minutes of my flight today…

…As we turned base leg to final suddenly I see the yellow bar rise up to the artificial horizon and the aural warning starts going off indicating we are “close” to the ground and that the gear is not down and locked.

The noise this aural warning system makes can be frustrating because it may block out radio transmissions since it is so loud, not to mention that it can be very distracting, especially when you are very busy and you know there is nothing “really” wrong. Luckily we were VFR so I knew we weren’t close to the ground. If we had been IMC, I would have most likely done a go-around, sorted out the problem and then gone back for another approach. So, like I said, since we were VFR, I call for “Gear Down.” This eliminates the warning but then I get another warning, “Don’t Sink.” The airplane, i.e., RA, thinks that we are descending too quickly. Completely erroneous since I’m on a stabilized approach. Then, when I get to 500′, my first officer realizes that we didn’t get the “500″ aural callout, but goes ahead and runs the final checklist anyway. Finally, we get down to 50′, when we are suppose to get callouts for the last 50 feet of flight in 10′ increments. At about 20′, I realize that I’m not getting the callouts, which is usually the clue to reduce thrust to idle and flare the airplane, so I just fly normally and land. No problem. It was actually a decent landing!

Now this may not sound too demanding to you, but let’s put this into perspective. You are flying into ORD…one of the busiest airports in the world where instructions and clearances come at you rapid fire not to mention that you are landing only about 3 miles behind the airplane in front of you. Furthermore, 22R is one of the shorter runways in ORD so you have to land spot on and the airplane lands at about 130 knots. Throw this annoyance into the mix and things happen pretty fast.

Well all ended well and that is the most important thing…

To Your Flying Success…

Jeffrey

Jeffrey is a captain at a regional airline and flies the CRJ200, CRJ700, and the CRJ900. He has over 4000 hrs of flying experience in many different airplanes and is a Gold Seal flight instructor to his credit. He has recently written “The CRJ200 Quicknote Study Guide” that simplifies the systems of the CRJ200 into a easy-to-understand, downloadable eBook. Click here to get your copy today!

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