Depressurization in the Flight Levels in a PA-46

You are flying along in the Flight Levels enjoying the cool, smooth air, when all of the sudden a loud report (bang) shakes the peace, the cabin altitude increases uncontrollably, and the temperature plummets.  Additionally, you find yourself breathing deeply…very deeply.  What should be your response?

The answer to that question is, “It depends”.  Similar to other emergency situations, many factors play into a successful handling of a loss of pressurization.  No emergency situation is identical, and there rarely is a “cookie-cutter” response to most emergencies.  An understanding of the aircraft systems, solid training, and good decision-making is required.

That being said, I see the “loss of pressurization” emergency butchered often during training, with an uncomfortably high percentage of pilots NOT responding in a manner which would ensure survival.  Most fidget with the oxygen/mask for WAY longer than is acceptable, with many never getting to the point where they are breathing O2 properly.  Some never start a descent (or they immediately start a descent without thought of other factors), and many don’t know the leading causes of loss-of-pressurization in a PA-46.

With this introduction, let’s discuss some of the more important factors related to a loss of pressurization event in the Flight Levels:

  • You must get O2 to your face: Knowing where the O2 is located and how to get O2 to your face is critical.  Whereas some pilots MIGHT be able to survive a loss of pressurization event without the use of O2, using supplemental O2 ensures a MUCH higher chance of a successful outcome.
  • Squat Switch: The #1 cause of a rapid depressurization in a PA-46 is a faulty Squat or WOW (Weight On Wheels) Switch.
  • Talk to ATC: Not only do you want any other aircraft below you moved out of your way, you want to use ATC as a resource to to help resolve your problem.
  • Go down:  You need to quickly plan a descent.  Your ability to provide O2 to your needy body tissues (especially the eyes and brain) improves exponentially as you decrease altitude.

With these truths fully understood, let’s add an understanding of the pressurization system on any airplane:

A rapid depressurization event can only happen through one of two causes:

* The pressurized vessel is compromised (window blowout, a hole in the cabin, safety valve inadvertently opening, door popping open, etc.), or:

* A fault with the incoming air that pressurizes the cabin (hose leak, bleed air failure, Cabin PRESS Valve pulled, etc.)

If you experience a rapid depressurization event, you must place the mask to your face and start breathing pure O2.  You should know where the mask is located, ensure it is located at a readily accessible location, and know exactly how to ensure the O2 is flowing.

Meridian pilots have an additional concern…the mask on a Meridian is simply not a good fit (pun intended!).  It is designed to be a “quick donning” mask, and there is no doubt you can put the mask on quickly.  But, there’s no way to get the mask on without knocking off the headset and glasses (a high % of PA-46 pilots wear glasses while flying).  So, if the Meridian mask is placed on the face via the “quick donning method”, it renders the pilot unable to see well and unable to hear ATC without pushing buttons (which he probably won’t be able to see!).  I see Meridian pilots fumble this situation more than any other, and this is because the mask completely limits their ability to handle the other important aspects of a loss-of-pressurization event.

My recommendation in a Meridian is to turn ON the O2 lever, and simply place the Meridian O2 mask up against your face with the right hand (without putting the bands on the back of the head) and breathe normally.  Then, the Meridian can be flown with the free hand.  If the second hand is needed short-term for flight, just set the mask down and accomplish whatever task is required of the second hand.  Then, get the mask back up to the face quickly.  It is amazing how quickly the O2 gets to the cells in the body after a mask is used.  If you have a Pulse-Oximeter, do some personal testing at lower altitudes to see how your body reacts.

If you experience a compromised pressure vessel (blown window, door, etc) or a mechanical problem with the incoming air (duct failure, etc), there’s no way to repair the situation and you must deal with the emergency by descending.  I’ve had a pilot side window blow out in a PA-46 before (here’s the story) and I’ve had an incoming air duct blow free.  On both situations I could not “fix” the problem in flight and had to deal with a broken airplane.

But, if you don’t perceive an obvious major structural problem, the most probable cause of the depressurization is a faulty Squat Switch (Weight On Wheels Switch).  In fact, the Squat Switch is BY FAR the most probable culprit in a PA-46 depressurization…so much so that a prudent pilot should remove the Squat Switch from concern by pulling the CABIN PRESS Circuit Breaker (CABIN PRESS DUMP in the Mirage/Meridian) immediately after a loss of pressurization.  If the cabin altitude begins to descend after pulling this CB, you’ve solved the problem and can continue your mission.  The cabin will descend at the rate selected on the Cabin Rate knob, so turn the Cabin Rate Knob (the one with the arrow) fully clockwise to ensure the cabin descends quickly. The CABIN PRESS CB should be one of the CB’s that is collared (so you can find it easily) on every PA-46, and every PA-46 pilot should know exactly where it is located in their airplane.  Pulling the CABIN PRESS CB ensures the Safety Valve will CLOSE.

A quick systems lesson…the Safety Valve is opened by vacuum, and the vacuum is controlled by a Solenoid Valve which is controlled by electrical energy via a wire going to the Squat Switch (and also the Cabin Dump Switch).  By either landing the airplane (allowing the landing gear to close the Squat Switch) or by the pilot pushing the Cabin Dump Switch, electrical energy is APPLIED to the solenoid allowing vacuum to OPEN the Safety Valve.  A pulled CABIN PRESS CB breaks the circuit between the Squat Switch/Cabin Dump Switch and the solenoid, automatically closing the Safety Valve.

Pulling the CABIN PRESS CB should take you no more than a couple seconds, and your next job should expend only a few seconds too…you should immediately call ATC.  It doesn’t have to be flowery, long, verbose, or even two-way communication…and it does not need to be a request for permission.  All you have to say is something like this, “N12345 has lost pressurization”.  Controllers are taught to recognize pressurization problem situations and their job will be to move other airplanes out of the way from you.  That simple communication will set in motion a series of events that will go MUCH smoother (and safer) by allowing ATC to be a part of the solution.  Don’t worry about declaring an emergency (yet, unless needed), don’t worry about causing others trouble, don’t worry about answering him back and explaining the minutia of the situation, don’t worry about saying it wrong…just squeeze the trigger say something to ensure they don’t have to wonder what’s going on in your cockpit.

Next, quickly plan a descent.  Notice, I did not advise that a descent be started as a matter of absolute requirement.  Going down will certainly help the pressurization problem, and it’ll be required eventually for sure.  But, sometimes an immediate descent is not the most prudent action.  Since you are breathing O2, you are not in a dastardly situation, and a quick look at the weather, terrain, and traffic below can make the soon-to-happen descent MUCH more safe for everyone.  Icing conditions below? Over high terrain?  Any airplanes below you that need to be diverted first?  Once you make a quick plan based on actual conditions, then it is time to start the descent.

As you consider this emergency and rate of descent required, remember that a PA-46 operates in the “lower flight levels”.  A loss of pressurization event in a jet at FL410 is a VERY different emergency than a Malibu that looses pressurization at FL200.  Your Expected Performance Time (EPT) is exponentially LESS as altitude increases. Consider this chart and get an idea of how much time is required for a pilot to act upon the emergency.  A jet at FL410 has only seconds to react or die, a Malibu at FL200 has over 10 minutes.

Expected Performance Time Chart

I recommend the pilot start the descent by turning off the autopilot and hand-flying the airplane.  The landing gear should be DOWN and the throttle brought to idle. With the throttle at idle and the gear DOWN, most PA-46’s will descend at 3,000+fpm if flown at speeds on the upper end of the airspeed indicator. If a faster rate of descent is desired, a bank can be established.

Once these critical factors are considered, then there’s plenty of time to consider other less-important factors:

  • Pull out a checklist: This should be ready and available in flight.
  • Set the Flight Director: Even thought the Autopilot is OFF (because you turned it OFF to properly initiate the emergency response), the flight director should be set for an appropriate descent rate and then a lower (and appropriate altitude) should be put in the Altitude Preselector so the pilot will be commanded to level off at a lower altitude.  This way, only one button is required to reestablish proper Autopilot assistance, if desired.
  • Consider the cabin occupants: If onboard, they’ll be in the back wondering what’s going on.  Give calm assurance, but maintain your priority of flying the airplane.  They will be just fine, even if they don’t get a mask to their face.

No loss-of-pressurization situation is identical, and…as in every emergency situation, a pilot must use the balance of knowledge, experience, and available tools to handle the emergency.  My hope is that this discussion helps someone handle a loss-of-pressurization emergency in a PA-46 a little better and a little safer.

About Joe Casey

ATP, CFI, CFII, MEI, CFI-G Commercial Pilot - SE, ME, Rotorcraft, Glider US Army AH-64 Pilot and UH-60 Instructor Pilot and Instrument Flight Examiner
This entry was posted in Flying Techniques, PA-46 Airframe systems and tagged , , , . Bookmark the permalink.