Tag: IMC

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Understand how to use VOR and ADF Nav aids to orient yourself anytime

VOR cessna 172 flytime

Nav aids like the VOR and ADF are there for you to use anytime you should need them. Having a solid understanding of these navigational (nav) aids is important and goes beyond training offered to us as private pilots, but is available for us to learn to become proficient aviators, particularly if we are regularly flying long distances, with passengers, at night, or any combination of those.

Basic nav instruments can be valuable

In a typical aircraft used for flight training, usually a Cessna 172, we’ll often have a VOR, ADF and GPS.  When we’re training for our private license, we typically aren’t introduced to these tools, but we do learn about them briefly in ground school. In commercial training, we learn about all of these in more detail and must become proficient at them, as we’re expected to demonstrate their use on a flight test. But it should go beyond that. Even if you’re not training for a commercial license, you should be familiar with these nav aids and how to use them. In case the weather should deteriorate, particularly at night, you’ll be much safer.

These basic instruments can help you create a situational ‘mental map’ of your location, a mental map that will become invaluable should you get lost or encounter adverse weather and are forced to divert. 

Preparing for a worst case scenario

Having the simple, yet valuable information provided by these basic instruments becomes extremely important in case the worst should happen. What if you take off with a shaky forecast, and fly into some weather? We’ve all been told that if we head into clouds or low visibility we should note our heading and begin a 180 degree turn into the reciprocal heading.  But how about if we just loose visibility, flying into an area of low cloud or haze? We need somewhere to go, so how do we find it? We have to find a suitable place to divert to, and knowing where your ADF and VOR stations are on the map can help us get there. 

A flight instructor gave me instructions for a simulator session to use as training in these instruments. The exercise has many practical applications for flying in both day and night, as it helps orient you in reference to a station and an airport, to help get you land when you need to terminate your flight due to deteriorating weather. It’s better to try to land at an airport than planning a landing in a field. 

The VOR

The VOR transmits 360 single radials from a specific station. When you select a specific radial on your VOR instrument, you’ll be able to see which side of the VOR station you are depending if you see a “TO” or “FROM” flag.  For example, say you are lost somewhere in the vicinity of Springbank airport in Alberta, and you want to return to there and land. You’re not sure which way you should head to get back to your airport. Knowing the frequency for the Springbank VOR, you tune it and immediately you’ll be able to get information of which side of the station you are on and how you should track to get back there. 

Where am I?

Here is an example.

Once you tune your VOR to a station, select radial 150.

If it says TO, that means you’re on the other side of that radial. If it says FROM, you are on that side of the radial. 

The ADF

Your automatic direction finder, or ADF is a basic instrument that transmits location information on the AM band. To use, tune it to a non-directional beacon (or NDB). The arrow on the ADF will always point to the station. 

ADF flytime alicja gados
The ADF on a Cessna 172. The ADF always points to the station.

These stations will eventually be shut down in Canada, and Transport Canada has been planning to decommission the stations for years. This planned decommissioning is not happening quickly. They still remain, and will likely be around for years to come, and while they do, are a basic, though valuable navigational tool that you can use to orient yourself. 

Where am I?

To use, once you tune the ADF to the specific NDB frequency, listen for the morse code. That is how you know you have the right NDB. Now, note where the arrow points. 

The arrow always points to the station. To head directly to the station, align the nose of the airplane at the top of the instrument (0 degrees). To depart with the station directly behind you, align the arrow to point directly behind the airplane. 

A real life example

You depart Calgary/Springbank on a VFR flight with paying passengers heading north to Rocky Mountain House. The GFA shows a cold front moving through the area from the northwest with deteriorating ceilings and visibility over the next six hours.

On your way out to climb runway heading of 350 to 5500′, you intercept and track outbound of the Turner Valley NDB (299) and continue the climb to 6500′. 

From Calgary International, you can track the V306 airway (116.7) to track outbound (away from) Calgary towards your destination. On your way along the track, you can tune to the Sundre NDB and to track your progress also and report when you’re abeam the station (when you are passing the station on your left hand side). 

So, you know where you are and continue en route.

The ceiling drops. Now you have to descend to stay VFR. You descend to 4500′, taking note that there are towers in the area that are close to that altitude. Tune the Red Deer NDB (320), and use it to keep track of when you pass the James River, not abandoning the flight quite yet.

The weather gets worse  – it now becomes unsafe to continue, and no longer VFR.  Now you abandon your original course and aim for the closest airport – that is Red Deer. You’ve already got the NDB tuned to Red Deer, so you just turn and track direct to there, climbing back up to 5500′.

Enroute to Red Deer, you experience a vacuum failure. This means you’ve lost your heading indicator and attitude indicator, and you’re now flying partial panel, using your turn and bank coordinator as the best indicator of your attitude, cross referencing the airspeed and VSI to confirm. 

You’ll cross the Red Deer NDB at your altitude of 5500′ and begin a descending, rate one, right turn to get to runway heading of 345 (the runway you’re aiming for will be runway 35). This is a timed turn, so you’ll have to note your heading going into the turn and make sure your turn is consistently rate one throughout. Or else you may over or undershoot your runway, and you don’t want to spend any more time flying around in precarious weather with limited instruments. 

Once you land safely, there is great reason to celebrate. You have just used your skill to get your passengers, yourself, and your airplane down on the ground safely.

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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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Pilot Perception: Runway Illusions

On Final

The “softer” side of flying is the human factors side. As advanced as modern aircraft are, pilots are subject to various factors that can cause them to make excellent decisions and judgement calls but sometimes make decisions that can be potentially dangerous. Luckily, illusions pilots experience are well understood and documented.  We know when we may experience an illusion.  In instrument flying for example, we learn how to ignore what our body is telling us – for example, that we are in a steeply banked turn when we are in fact in level flight – we learn how to trust our instruments in IMC.   Sometimes the message our body is telling us can put us in danger if we subscribed to it.

We are governed by the messages our body is sending to our brain.  This affects our flying and our perceptions of certain situations.  When we are approaching a runway with a up or down slope, or when we are approaching a runway that is level but the terrain before the runway is up or down sloping, it is possible and expected to incorrectly plan our approach.

Runway illusions are very common in flying, and are the result of our brain telling us something other than what is actually happening because it is extrapolating on what it sees.

Runway slope illusions. Image courtesy of americanflyers.net
Runway slope illusions. Image courtesy of americanflyers.net

When a runway is upsloping, the pilot thinks that the runway continues on an upslope from the terrain before it, hence thinking the terrain in front of the runway is upsloping as well.   The pilot will judge their altitude as too high, because they perceive the terrain continues on an upsloping, positive angle towards the runway  and will consequently plan a low approach that can cause landing short of the runway.

The solution? When flying toward a known upslope runway, expect that you will perceive being higher than you actually are and plan to land long on the runway.

When a runway is downsloping, the pilot thinks that they are too low and will consequently plan a higher approach and land long on the runway, or may even have to overshoot.   This is again, because of extrapolating on the slope of terrain before the runway.  Thinking that the terrain continues on a downslope towards the runway, means that the terrain is actually higher away from the runway than on the approach path; so that the entirety of the approach path follows downsloping terrain.  The pilot will incorrectly judge altitude as being too low when in fact he is too high.

The solution to planning an approach on a downsloping runway is to anticipate feeling like you are too low and plan to land short of the runway.

Also, when the runway is level but the terrain before the runway is upsloping: the pilot will extrapolate the same way.  They will think the runway is upsloping as well, and be subject to the same upslope illusion, and should plan to land long.  Alternatively, when the runway is level but the terrain before the runway is downsloping, the runway will also be judged as downsloping, and the pilot should plan to land short to avoid an overshoot.

It is hard to memorize the concept but I found that a good way of learning and remembering the concept is to draw an upsloping or downsloping runway and flat terrain in front of it. Then draw a straight dashed line following the angle of the runway towards the approach path, and this will be the pilots perception of the approach terrain.   From there we can easily imagine whether the pilot will feel too high or too low in each situation.

Rain on the windshield can create the the feeling of greater height and haze can make distances appear greater than they are. This is a favorite Transport Canada exam question as well!

Wide and Narrow Runway IIlusion
Wide and Narrow Runway Illusion

There is also the classic, wide and narrow runway illusions.  When a runway is narrow, this creates the illusion that the plane is higher than it actually is, resulting in a low approach and possible land short of the runway. With a wider runway, the opposite occurs, we perceive the plane lower than actual, and can cause the pilot to flare too high or overshoot the runway.

Writing a lot of exams lately, I noticed that Transport Canada likes to test these topics!