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FlyingSafely.Com Surviving Vacuum Failure!!!!
On Primtime, August 30, 2001, there was a special investigative report done on
private plane vacuum pump failures and resulting accidents. Like much of the
press coverage of general aviation it was not a positive report. However, I must
confess that the point they made was very accurate and troubling. Vacuum pumps
fail and they fail without warning most of the time in most of our aircraft. When flying VFR this is no big deal because all you have to do is look out the window to tell which way is up. Not so when in the clouds. The pilots who lose control of their aircraft while flying in IMC are not novice pilots. They are trained, instrument rated, and some have thousands of hours of experience in all types of aircraft and flying conditions. One basic fact remains. Without the attitude indicator and heading indicator working properly, the chances of survival in instrument weather are not good. Below you may listen to actual ATC Recordings of Accidents in progress: (requires Realplayer). These are troubling but depict the seriousness of our problem. We are using a technology that derives from the 1930's when it comes to running vital instruments. Additionally, most general aviation aircraft have no warning device to indicate a failure. Instrument pilots are trained on partial panel, but part of that training is to avoid turns over 15 degrees. By the time the problem is detected, the aircraft has probably gone well beyond the limits of partial panel instruction. To make partial panel training more effective, perhaps that training should include recovery from unusual attitudes with no attitude indicator and no heading indicator. Maybe it just doesn't work. Okay, turn coordinator, airspeed, VSI, and compass, but these are indirect indications of what is happening to you. If it was easy to bring things back to straight and level with these, good pilots would survive. They often don't. Such an accident is almost always fatal because the plane is out of control at a high speed and a tremendous rate of descent. What can be done??? I am thinking of ways to help prevent such an accident in the event of a vacuum failure. Please help me if you have ideas. 1. First off, a warning light or flag that warns you if you lose vacuum is essential for safety. I need to know right away when the pump quits. Additionally, my mechanic moved the vacuum gauge over in front of the pilot on our Cherokee 180 so, at least, it can now be included in the scan. (Before it was completely on the opposite side of the panel.) Like many things, survival is dependent upon early detection. 2. We need a way to get the airplane back from the unusual attitude the vacuum failure has caused. The primary instrument we use to do that is the attitude indicator, and since the first one has failed, we need another one!! This means we need to install a redundant Attitude Indicator powered by a different power source. A doubly redundant electric attitude indicator costs about $1,700 plus installation and a little paper work from your local FSDO. No need to wait until there is a problem to turn it on. Let it run all the time and include it in your scan. When the vacuum AI differs with your electric AI, check the vacuum gauge. If it is at zero, cover the vacuum AI and Heading Indicator and fly with your perfectly functional electric unit. No switches to throw. 3. In addition to using the electric attitude indicator, you can confirm your heading by using GPS. I always confirm my heading when in the clouds with the GPS readout. It updates every second and is not subject to turbulence, as is the compass. Reading the compass (which always seems backwards to me anyway) is tough in the bumps. With the electric attitude indicator and the GPS track readout, you can fly with attitude and heading information intact even though the vacuum system has failed completely! 4. The use of an electric wing leveler or auto pilot while in IMC is not a bad thing. If the vacuum fails the auto-pilot won't allow the airplane to get into an unusual attitude. Since our plane doesn't have a 3 axis auto-pilot, so we back up our flying with an electric wing leveler. I have often wondered when pilots lose their vacuum instruments why they don't immediately go to their auto-pilot or wing leveler. Most of them work off a separate electrical gyro, which is unaffected by the vacuum status. The auto-pilot could keep things together till some VFR weather could be reached. Neither of the pilots in the program I saw thought to use their auto-pilot or wing leveler. Maybe they didn't have those features on their aircraft. When thinking of what to do, think auto-pilot! Then scan carefully. 5. Always have post-it notes or soap holders or instrument gauge covers immediately accessible to you. It's nearly impossible to ignore errant instrument indications. If you cannot provide vacuum to the instruments, cover them! 6. Get a vacuum failure light in your airplane. If you have a back up vacuum system and you know your engine vacuum pump has failed, then by all means engage it. Additionally, use your back up AI, your GPS for heading confirmation, your electric auto-pilot and practice doing this. 7. Be sure you have equipped your aircraft to give yourself survival options if your instruments or vacuum pump fail. The biggest challenge to the pilot is to recognize what has failed and then make the necessary adjustments. If you are flying IMC with no backup, get a loan (if necessary) and put the things in your plane that will give you a fighting chance. Until then maintain VFR. Larry, Editor FlyingSafely.Com Below are a couple of typical accident reports of aircraft accidents with inoperative vacuum or instrument failure. There have been 36 of these since the late 1970's. |
