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Instrument flying: flying with a partial panel

cockpit 1957 beechcraft airplane

The complexity of  flying on instruments increases when we simulate a vacuum failure. We loose one especially critical instrument necessary to our flight attitude coordination. The Loss of this instrument in flight can certainly and very quickly and easily turn into a life and death situation.

The purpose of partial panel training

The goal of partial panel simulation is simple: what would happen if you were to have a vacuum failure in the most critical time, when you were in IMC or flying at night? The reason for learning essential basics of instrument flying, including emergencies such as partial panel, doesn’t have to be so complicated as to just needing it to earn your IFR rating for airline flying. 

How the vacuum system works

The vacuum system is operated by a venturi which is usually engine driven. The change from higher to lower pressure drives the gyros, so these require some time to spool up and are only accurate after takeoff.  

The heading indicator and attitude indicator are vacuum system powered gyros and the turn and bank indicator are electrically powered. So in the event of a vacuum failure, you’ll be able to use your turn and bank indicator to assess when you are wings level and coordinated.

How can we end up with a partial panel in real life flying?

Since in airline flying you’d never encounter this situation, you can experience a vacuum failure at the worst possible as a private or bush pilot, or a pilot for a smaller operation that does bush flying in remote areas. There can be pressure to complete a job, pick up passengers, or get people to a certain destination. You know the weather is going to deteriorate but you decide to go anyway. You fly into the front which has come earlier than forecast and end up in a situation where you are pushing the weather.

Deteriorating weather

Picture you’re on a night cross country flight with little to no great reference to the ground. You’re essentially flying on instruments. Or, you’ve departed during day VFR with a sketchy forecast, and you’ve inevitably flown into an area with low ceilings and decreasing visibility. It starts slowly at first, and before you know it, you can’t see the ground, and you don’t know which way is up.  If the worst was to happen and your vacuum system loses suction at this time. You’ll be in deep, trying to keep the airplane under control while trying to figure out what the heck you need to do to get yourself out of this situation.

The first thing you do, of course, is be prepared for this type of worst case scenario by practicing these difficult situations under the hood or better yet, in the simulator. You can even practice at home. Have your instructor create a scenario for you where you are flying to an area with a less-than-ideal forecast tracking different VOR radials and NDBs, and along the way simulate slowly diminishing visibility until you are forced to divert. Enroute to your diversion aerodrome you loose your vacuum system, and are forced to fly without your AI and HI. You need to get to your airport and out of this mess. 

Cessna 182 in northern alberta
Cessna 182 stuck at a snowy airfield in Northern Alberta.

1. Don’t panic – fly the airplane

The first thing you do if this happens to you is to remain calm, and fly the airplane. Remember to always aviate, navigate and then communicate, in that order. Always focus on flying the airplane before you do anything else. This is especially true when you’ve found yourself in a low visibility situation with limited instruments. 

Focus on the instruments that give you the information you need, and start your scan. In the case of full panel flying, this is a lot simpler because you have your attitude indicator at the center of your scan which gives you your most critical information: the position of your airplane against the horizon. Are you nose up or nose down, and are your wings level or are you in a turn?

Start your scan

When you lose your vacuum system, your gyros, the heading indicator and attitude indicator will be immediately unreliable. The major challenge with this is that these two instruments, particularly the attitude indicator, are at the center of our scan. So we have to quickly develop a new method. 

The main concept continues unchanged, you continue to control the aircraft with the formula attitude plus power equals performance.  The difference is now you have to look at other instruments to get this information. When flying without an attitude indicator, you must determine your pitch by primarily referencing your airspeed indicator, and verifying it with altitude and vertical speed indications. 

Control Instruments

Attitude: Airspeed Indicator

Referencing your airspeed indicator for pitch is challenging but doable and requires significant practice to master. My instructor set up a scenario in the sim where my vacuum system failed in cloud while on a low-level diversion to Red Deer. I flew this route a few times and found it took a few minutes to organize the scan before I got the aircraft into a reasonable state of control. The important thing is not to chase the instruments. I did this at first, and found my airspeed all over the place, and then my altitude started to fluctuate and I descended to only 500 AGL. 

This happened because I was not allowing the airspeed to stabilize. A certain attitude will give you a certain airspeed. Let it stabilize and reference your altitude and VSI to ensure you’re at a stable straight and level attitude. 

Turn information: Turn and Bank Coordinator

Use the turn and bank coordinator to verify that you are wings level. Use the magnetic compass to verify the heading has not changed. Do not fly heading via the magnetic compass, it’s too confusing. The compass works in the opposite direction to turn. So unlike a heading indicator, you turn away from the heading you want to go to, the opposite response that makes sense. The compass also has a significant amount of lag. It’s only reliable to verify that we are on the proper heading, but not looking to it as a control instrument. 

Your performance instruments

The performance instruments help you verify the impact of your control inputs are or aren’t what you want them to be. In partial panel flying, they are always attitude plus power equals performance:

Attitude + Power = Performance

Control Instruments + Power = Performance

Airspeed Indicator + RPM = Outcomes shown on the VSI, Altimeter and Magnetic Compass

Turn and Bank Coordinator + RPM = Outcomes shown on the VSI, Altimeter and Magnetic Compass

2. Navigate 

Find out where you are by using VORs, NDBs, GPS or ideally combination of those. You can also ask for vectors. This of course bring us to:

3. Communicate

Let air traffic control know you’re in an emergency and ask for help.

Next find out how to use rated turns to get yourself out of cloud and into an airport. Executing a timed turn is a critical skill and becomes very important during partial panel flying.


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The Forced Approach and Landing

Forced Landing of TACA Airlines Flight 110. Image Courtesy of

So now that we know about the precautionary procedure, what happens if we have NO engine power?

We plan a forced landing! The image above shows an actual forced landing of a Boeing 737 jet. TACA Airlines Flight 110 lost power in both engines and successfully glided and landed on an unprepared, makeshift field (image courtesy of

Is planning a forced landing possible?

For those who believe that a successful forced landing is difficult or impossible to achieve, Transport Canada’s “Flight Training Manual” (FTM) reminds us that for glider pilots every landing must be a successful forced landing. Hence, it is not only possible that it can be done, it can be done well.

Yesterday I went through the basics again with my instructor.  Each instructor has a different way of teaching, so the method will vary slightly for everyone.  The basics are more or less the same.

Famous Forced Landing: The ditching of US Airways Flight 1549 into the Hudson River. Image Source:
Famous Forced Landing: The ditching of US Airways Flight 1549 into the Hudson River. Image Courtesy of

The most successful recent emergency forced landing was US Airways flight 1549: a ditching in the Hudson River. After multiple bird strikes into the engines caused dual engine flameout,  the gliding Airbus A320, which didn’t have enough altitude to return to the airport, was successfully ditched in the Hudson River. Like all pilots, trained in forced approaches, he captain used the same line of thinking that we are taught when learning how to execute a forced approach and landing.

We are flying along – and – we’ve lost engine power! What is the first thing we do? We fly the plane.

(1) Best Glide Speed

We have to establish our aircraft in “best glide speed.”  For the Cessna 172, this is 65 knots. The best glide speed provides the maximum “lift to drag” ratio and allows the airplane to glide as as long as possible.

(2) Best Field

Now we have to look outside and quickly locate the best field where we will put our aircraft.  We locate this field, and turn towards it.  Look for indicators of wind direction on the ground, and make your best efforts to land into the wind. If in doubt of wind direction, simply plan to land in the same direction that you took off from the airport.

Make sure to do a good check of the suitability of the area for landing. This means: check for civilization, obstacles, wind, field length, and landing surface – abbreviated the COWLS check.

(3) Fault

Now that we have our field chosen and have established our glide, we have some time to do some quick engine checks to try to determine the cause of engine failure. Often, with carburetor equipped aircraft such as the Cessna 172 the engine can die due to carb icing.  Or if we descend from a higher altitude and we fail to richen the mixture. These quit simple steps will attempt to reestablish engine power and will not cause us to loose too much time and altitude.

Fuel Selector Valve: Both

Mixture: Full Rich

Carb Heat: On

Ignition: Both

If it doesn’t start, we simply shutdown the engine using the same steps as above:

Fuel Selector Valve: Off

Mixture: Idle cut off

Carb Heat: Off

Ignition: Off.

The above three steps should take us about 500′ of elevation loss to do. Since this is a simulation … we do an engine warm up by adding 200 or so RPM.

(4) Mayday Call

Before we get too low we make the Mayday call. We say “Mayday” three times and our aircraft identifier three times (just like in the case of a precautionary landing).  Broadcast your location, your intentions of where you plan to put the aircraft, the nature of your emergency, and the number of people aboard.

(5) Passenger Brief

Let your passengers know: to put their seat back, stay clear of flight controls, put away all sharp objects, and so on.  You can let them know where the ELT and fire extinguisher are.  Also, it is important to ask them to unlatch the door prior to touchdown.

If this landing is on an unprepared surface, your landing will be a soft field landing.

Make sure to assess how the prevailing winds will affect your approach and landing. What are the upper winds doing?  Also state that you intend to touch down on the first third of the field.  For the Cessna 172, we touch down slightly tail low and turn off the electrical as instructed in the POH.

Successful Forced landings

Another example of a very successful forced approach is in the case of Taca Airlines Flight 110 on May 24, 1988. After flying through severe thunderstorms, the jet lost both engines that the pilots were not able to restart.  In the perfect moment the captain found a grass field and pointed the giant gliding 737 towards it. He was able to land successfully with no loss of life and minimal aircraft damage. In fact, Boeing engineers were able to do the necessary repair work on the spot and the aircraft was flown from the very spot where it was landed! Watch the video of the incident below.

Read details of how to plan your approach and land in your desired touchdown spot. This is the low key / high key planning procedure.