Whether you use a pressure or vacuum system, the loss of your pneumatic system in IFR conditions can provide you with a very challenging last couple of minutes of your life — and a pneumatic system failure can occur at any time.
FIRST RULE: FLY THE PLANE. If you are on instruments and your gyros fail, switch your scan immediately to alternate instruments. Use your turn coordinator, airspeed, altitude and compass to regain or maintain a normal attitude — and if you have a GPS, use it!
To Control Pitch: Watch for increases in your airspeed accompanied with decreases in your altitude. This indicates a nose low condition — which must be corrected to avoid over speeding the plane and causing structural failure. Accordingly, decreases in your airspeed accompanied with increases in your altitude indicate a nose high condition, which must be corrected to avoid a blind stall. Be very aware of your trim tab and the flight characteristics you should expect for its current setting.
To Control Bank: Use your electric turn and bank or turn and slip indicator, to keep the wings level and use your compass and GPS to maintain a heading. Note: if there is any turbulence at all, the compass may provide more distraction than help. Watch for changes in rate-of-turn and make corrections to unintentional banks immediately with smooth control inputs.
GET HELP – As soon as you obtain stable control, punch the button on your microphone, declare an emergency and inform ATC of the nature of your problem. Once ATC knows of your situation, they will be better able to inform you when your flight path degrades from the normal, such as an unexpected climb or descent, or an unexpected change in course. They will also move other traffic away from you and may be able to vector you to VFR conditions if they exist nearby. Be sure to take full advantage of any assistance that ATC can offer, but do *not* wait for permission to do whatever you feel is necessary to keep the plane under control. Stay alive.
COVER THE DEAD INSTRUMENTS. All you need to do is glance at a dead instrument once and you can get confused, distracted and make mistakes. Using post-it covers, soap dish covers with suction cups, even gum and paper will block the instruments and their faulty information from your scan. Always keep something in your flight bag you can use for this.
GET DOWN TO THE GROUND – FAST. The real scenario is never this simple. If instruments fail in IMC, you may have a *very* hard time distinguishing what’s working from what’s not. The safest place for you, your passengers, and your plane is on the ground.
BEST DEFENSE. If you lose gyros in IMC close to the ground, while maneuvering or after take-off, the chances that you’ll figure out what’s going on and respond appropriately are very slim. A thorough ground check of instruments, including listening for the electric gyros to spool up when the master switch is turned on, watching your pressure-driven gyros when the engine starts and checking vacuum pressure during your run-up will give you an edge. If you make these steps a habit, your ears and eyes will become accustomed to what’s normal and you’ll have a better chance of catching what’s not. Stay sharp, stay focussed during preflight and in the air, use what you know, observe your aircraft and learn something from it every time you fly. It might just save your life.