S Turns

It should be as easy as crossing the street right?

Learning to fly may be fun and exciting, but the process is anything but. That compounds when it comes to flying ground reference maneuvers. Most of the most common problems stems from the fact that we must divide our attention between multiple tasks as we constantly make adjustments to keep the aircraft on the right ground track. A few have virtually no problems, but most find it both a challenge and a struggle.

Ground reference maneuvers are both important and necessary. The skills you learn from are necessary in many portions of flight, but most importantly in your landings. And come on, after all, landing is the ultimate ground reference maneuver, requiring precision, rapid corrections, and smooth coordination of the flight controls.


When i was learning, besides landings, the second most difficult ground reference maneuver was S-turns.  During this maneuver, we fly a series of CONSTANT-RADIUS S-turns along a reference line.  The problem that i encountered was mastering the proper entry, and did not fully understand to connection between bank angles, and wind drift.  Once i started to understand how one effects the other, i was able to learn to fly this maneuver without any trouble.

How we enter

Before we do anything, we have to get ready.  Checklist, Configure the aircraft, Proper altitude, Clearing Turns.  Remember clearing turns.  You want to ENSURE the area is clear of traffic.  Doesn't hurt to be on flight following when doing maneuvers.  We need to enter this on the downwind, just like any ground reference maneuver; landing, turns around a point, turns around a rectangle (Landing Pattern?)  If we don't enter this maneuver on the downwind, it will definitely cause a flux of problems with the maneuver.

Are you wondering why we need to enter this on the downwind?  It allows us to establish the proper maximum bank.  But the problem is we need to know where the wind is coming from, to enter on the downwind.

Most common misconception

That doesn't mean if we enter on the downwind, we have nothing to worry about.  If we don't understand the maneuver we will continue to have problems.  Those problems are when to increase and decrease the bank angle to keep on our CONSTANT-RADIUS, and keep us where we NEED to be.


It makes sense that when flying crosswind on the downwind side of the road, the wind is blowing us away from the road, and that we would need the greatest bank angle to get us back to the road.  It also makes sense that when flying crosswind on the upwind side of the road, the wind is blowing us towards the road, and a steep bank angle would help us complete that portion of the turn more quickly.  The simple fact is that flying the S-turns by this logic will cause us to fail each time.

How do we do it?

To succeed in this we MUST understand the relationship between rate of turn, bank angle, and ground speed.  To understand S-turns, we will talk about a less-complex maneuver; turns about a point.  The point of this is to fly a CONSTANT-RADIUS, CONSTANT-ALTITUDE turn around a reference point somewhere on the ground.

I have a fast car, so this is how i think of it.  Imagine a race car going around a circular track that is two miles in circumference.  If this race car is going 60 mph, the car will complete a lap around the entire track in two minutes.  Since the car completes a entire lap in two minutes, the rate of turn for the car is 360 degrees every two minutes, or 3 degree per second.  Now lets take that same race car, on the same track, and punch the throttle, till we get up to 120 mph.  Now we are really moving.  This car can complete a lap in 60 seconds.  Our rate of turn would be 360 degree per 60 seconds, or 6 degrees per second.  Now the rate of turn required to complete a full lap over the ground depends on speed.  The faster the speed, the greater the rate of turn.

So lets take that same race track, and fly over it.  (Not while spectators are there.  They might get a little scared.) Lets fly over it at between 600 and 1,000 feet AGL.  If we were flying at exactly 60 mph on a perfectly calm morning, we would need a rate of turn of 3 degree per second which is a standard rate turn according to the turn and slip indicator, to stay over the track.  If we increase our speed to 120 mph, we would then need to keep a rate of turn of 6 degree per second to stay over the track.  Remember from above, increasing the speed to 120 mph requires a rate of turn of 6 degree per second.  But remember when selecting your airspeed, remember to not exceed Va (Maneuvering speed). For your check ride as well as your practice, keep within PTS standards, which is +/- 10 kts.


The angle of bank we use controls our rate of turn.  The steeper the angle of bank, the greater rate of turn is achieved.  Now remember from above, the rate of turn depends on our speed.  And remember the bank angle controls our rate of turn.  The faster we fly, a greater bank angle is required to keep the same rate of turn.  The bank angle should NEVER exceed 45 degree.  


When we fly we usually never get a calm no wind day.  So lets spice this up a bit.  It's a windy afternoon.  We are flying over the same race track.  Our ground speed is going to change constantly because of the wind.  So we would in turn have to change our rate of turn, to keep over the track.  We change our rate of turn by using the bank angle.  As the ground speed increases, we will be forced to increase our bank angle.  As the ground speed decreases, we will be forced to decrease our bank angle.  Our ground speed will be the most when we are ...  Anyone?  Anyone?  downwind.  That is the point when the bank angle needs to be the greatest.  That is why we start this on the downwind.  We roll into our turn when abeam the reference point, and now we know each of the remaining point in the turn, our bank angle will be less that it was when we started.  When the nose is pointed into the wind, ground speed is low, and the bank angle is the least.


S-turns can be through of as a series of turns about a point, but simply split in half roughly upwind and downwind, then linked together end to end.  Again we enter downwind and establish our maximum bank angle as the reference point (the road) passes beneath the wing.  The bank angle will decrease to a minimum when we recross the road headed upwind.  When we cross the road, we only for a second, roll the wings level, then establish the bank in the opposite direction.  The bank angle slowly increases as we complete the next 180 degrees of turn, reaching the maximum bank bangle as we cross the road.  Again, we roll the wings level just for a second, and then roll into our maximum bank in the opposite direction and continue doing this over and over.

Other problems

Too often we can be fooled into thinking we fly a lot better than we really do.  This can also be the case in S-turns.  In light or calm wind, flying S-turns will make you think it's easy, and your doing perfect.  But that is because you cant see your mistakes.  To make these mistakes evident, try to fly S-turns in a 10-15 knot wind, that is blowing virtually perpendicular to your reference line.  With this wind, you will need to make the proper corrections, and any mistakes will start to be visible as deviations in your ground track.  After all your trying to fly a CONSTANT-RADIUS turn.


Since flying S-turns can be likened to a series of turns about a point, we need to pick points along the way as we fly the maneuver.  If our points are too close, we will try to use excessive bank angles and rush the maneuver.  That would end up sloppy at best.  If our points are too far away, the turns will become too big and the banks too shallow.  In general, the reference points selected along the reference line should be separated by about 3/4th of a mile.  Add a little more distance if we are flying faster, and a little less if we are flying slower.


During the check ride, look out for diversion and distractions while flying this maneuver.  Some instructors will attempt to distract you by asking innocuous questions about features on the ground, or features of the airplane, or questions about the instruments, or engine. (Is it normal for the ammeter to read five amps?  Why is there more fuel in one of the tanks.  Whats the altimeter setting?).  Some may even simulate an engine failure during this, just to see you have a hold of the airplane, and the situation.  So bottom line is divide your attention, don't get distracted, and above all be prepared.  I even read of one instructor dropping his pencil and asking the pilot to help him grab it while they were performing this maneuver.  Expect the unexpected!

Tie it all in!

Those are the key elements.  As long as we remember those elements we will be able to gain control and keep flight under control and coordinated.  So lets review.  There is more to this maneuver than just keeping the correct ground track and altitude.  We must also maintain situational awareness as we fly.  This involves looking for traffic, monitoring the traffic, and being prepared for emergencies.  


TO begin we must know where the prevailing surface wind are coming from.  Next, we have to select a suitable ground reference that is a relatively straight line perpendicular to the wind.  This can be a road, river, shoreline, power lines, railroad tracks, or any other reference that is similar.  We start ourselves about a mile upwind of our reference, we then get the aircraft to the desired speed, and complete any checklist that we have.  Do out clearing turns to make sure the area is clear of traffic, and if we are not already at our altitude, descend or climb to the required altitude, most of the time 600 - 1,000 feet AGL.


When we are ready, we will head downwind straight for our road, river, or what ever reference we are using, and as we cross it at a 90 degree angle, we pick a point along the road to use as a reference for the first 180 degree turn.  We roll into our bank of 30-40 but never above 45 degree.  Watch the reference point as we slowly roll out the bank to maintain a constant radius from the reference point.


We would crosscheck our speed, altitude, bank angle, and occasionally the engine instruments.  Keep an eye out for traffic, as well as possible emergency landing sites, just incase something goes wrong.  


As we fully complete our first 180 degree upwind turn, we should have the minimum bank angle, and we should cross the reference line at a 90 degree angle.  Before we roll level across the reference line, we need to be sure to check again for traffic, and any obstructions in the direction in which we will be turning.


Once we cross the reference line at 90 degree we would momentarily level our wings, and pick our next reference point, as we roll into the next turn.  We would cross check our speed, altitude, and engine instruments, along with traffic, as we increase the bank slowly to maintain the CONSTANT-RADIUS from the reference point.  We should once again be in our max bank of 30-40 degree before we cross the reference line a second time.  As we cross the reference line again, we would roll the wings level momentarily, and pick our next point, and then roll into the maximum bank in the opposite direction.  


We continue to do this back and forth.  Sounds easy?  Maybe too easy?  Well, after some understanding of the principles behind all of this, and some practice, this should be as easy as crossing the street.

Night Xcountry KAPV KCCB

The flight for our night xcountry was schedule for Friday, at 7:30.  For this flight we had to go further than 100 miles, and I still needed 4 landings to complete the requirements of 10 night landings.  So we were going to fly to Apple Valley and perform 3 landings there.  While in route we would do some hood work to get the requirements met.  That would put the 92 mile trip well into 100 with the hood work we were doing, and changing course to compass headings.   Then come back to Van Nuys and do the 4^th landing there at our home field.  I think he chose Apple Valley for a few reasons.  There is terrain around there that I need to be wary of, there is KVCV airspace right up on KAPV.  Additionally one of the runways is closed at night, so that should make it a little easier (I don’t think mike expected me to know that.  He was impressed when I told him that they runway was closed at night).  The proposed flight would take us from Van Nuys, north to Magic Mountain (VPLMM), then track the 053 degree inbound radial to the Palmdale VOR (PMD), at which point, we would the track the 081 degree outbound radial, to just past Southern California Logistics (KVCV).  Once out of KVCV airspace we would descend, while entering crosswind into the pattern, then I would continue downwind, at which time our altitude should be pattern altitude.

So by 6:30 I had the weather.  There were thunderstorm cells all over the place.  But they were at 15000’, so we were going to be well below them.  Most of the storms should be just north of our route, or to the west, and I was fine with both of those.  I’m glad we have the g1000 for this trip, as it has topology, so I can see if I’m close to any terrain around us, and we have the NEXRAD as well, so we would be able to monitor the weather.  I was at first iffy about the trip, as I was not comfortable with the weather, but mike ensured me it would be fine, and at first sign of deteriorating weather we would turn back.  We did not want to climb over mountainous terrain with downdrafts from the storms.  So we had it as a readily available option to turn back at any time.  So I felt better about it at that point.  I also did not hear once during my call to WXBRIEF “VFR NOT RECOMMENDED”.  They just told me about all of the thunderstorms around the area, and any Sigmets/Airmets that were current. 

I met mike at the airport at 7:30 and soon I was doing my preflight.  The plane was fine, although it was hard to see the oil level in the dark with a flashlight.  I think the oil was just changed, as it was almost clear color.  Although with the touch of my finger I could feel the oil was between the 6 and 8 on the dip stick.  I was also using just a blue/green/or red light as I did not want to look at or have a bright white light anywhere close to me to screw up my night vision, so that might be why it was so hard to see on the dipstick.  Soon we were inside to start her up, and I took an extra 5 minutes to get the AFD in the front pocket, all pens and flashlights in a place that I could easily find in the dark, as well as getting my flight plan, and sectional charts in order and in the correct places.  I got my checklist in the front pocket as well.  Ran through the checklist, and we were ready to go.   Contacted tower and was told to stand by for landing traffic.  Once I heard that, I turned off the taxi lights and just kept on the beacon and nav lights.  I did not want to blind the landing traffic. 

We were cleared for a right downwind departure at the flood basin.  We climbed to 2000’ and maintained altitude until we were out of Burbank’s airspace.  Then we initiated a climb up to 5500’.  This would get us over the mountains and leave us with sufficient room of buffer from the mountains.  At the Newhall pass, we turn to start and follow the 14 freeway.  It is the lowest point going through the mountains, and if we lose an engine, we have something to land on, rather than mountains and darkness.  This is one of mikes biggest things about xcountry is making sure to ALWAYS have somewhere to put her down if needed.  He is always telling me on my xcountry solo’s to always have somewhere in mind at all times, that I can put her down if needed.  Because you never know when to expect a failure and you always want a way out in those cases.

During this entire time, we are seeing the lightning strikes everywhere in the sky.  Just about everywhere you looked, you would see lightning cutting through the clouds and lighting up the sky like it was day time for a slight moment.  Then back to darkness.  It was unnerving, surreal, and beautiful all at the same time.

Once we got to 5500’, Mike tells me, put on the hood.  I ask him to take control the aircraft as I put it on.  But we have to make sure who has the airplane.  Once I asked him he said “Sure.  I have the airplane”.  I then repeated “You have the airplane”, and then he repeated “I have the airplane”.  You ALWAYS want to do this 3 step procedure, as to ensure positive transfer of control of the aircraft by someone.  I told mike, he had the airplane, he told me he had the airplane, and I repeated so he knows I heard he has the plane.  Then I let go of the controls.  I did not release until that was complete, as I wanted someone to have control of the airplane at all times.  This is a MUST in your check ride as well.  The examiner likes to see that someone is in control of the plane at every moment, and that you both know exactly who is controlling the aircraft.

I put the hood on and he gives control of the aircraft back to me.  He then puts a little twist on it.  He takes a wash rag, and covers the PDF and says I just had a failure of the PDF.  I don’t think he was expecting what I did next as it caught him off guard.  I push the red reversionary mode button and brought the PDF to the MDF screen.  He tells me that’s cheating and takes a wash rag and puts it over that one as well.  CRAP.  Now to the standby gauges.  Now all I have is the Attitude indicator, airspeed, altitude, and the compass. 

This was my first time flying with the compass.  He tells me to turn to a 050 heading.  I turn to what direction I think I need to turn to get there on the compass and the compass goes the opposite way.  So the compass is backwards.  If the number is to the right, you need to go to the left to get to it.  Then he asks me when the compass is accurate.  I told him in un-accelerated straight and level flight.  Correct.  Then he asks if I turn to different headings what the compass would do.  I knew of ANDS and NOSL but did not know about UNOS.  These are the deviations of the compass during flight.  *Note these are for the northern hemisphere:

ANDS: Accelerate North, Decelerate South.  So if your speed up it will show a heading change to the north.  And decelerate will show a heading change to the south.

NOSL: North Opposite, South Lead.  If you turn from a north heading, the compass will initially show a turn in the opposite direction, and then catch up.  If you turn from a south heading, the compass will initially show a turn in the correct direction, but at a much faster rate than is actually occurring.

UNOS: Undershoot North, Overshoot South.  If we turn to a north heading, we need to undershoot our compass heading by about 30 degree for north.  If we wanted to turn to 45 degree heading we would undershoot by about 15 degree.  And on east/west we do not under/over shoot.  If we turn to a south heading, we need to overshoot our compass heading by about 30 degree for south.  If we wanted to turn to 225 degree we would overshoot by about 15 degree.  And on east/west we do not overshoot.

Mike told me a good way to remember which way to turn.  It’s like a clock.  If you want a bigger number in the heading turn clockwise.  If you want a smaller number, turn counter clockwise.  That helped a lot while I was flying to think about it that way.  It much easier to remember something, when you can relate it to something you are familiar with.    We did this for about an hour, turning back and forth to different headings.  The entire time though, we stayed within 100 feet of our altitude, and stayed practically right on our headings. 

Mike asks me to take off the hood, which I do.  Then he asks me where we are.  He zoomed out the GPS screen so I can only see we are in California.  But was uncertain where we were exactly.  So I use my trusty sectional chart.  I took at a VOR that is in the area of where we are, and find out what outbound radial we are on.  Turns out we were on the 081 degree radial from the PMD VOR.  Then I tune the EDW VOR and find out we are on the 150 degree radial.  That means we were just due east of Gray Butte Private airfield.  We zoom into the GPS and sure enough, we were only a few miles from the airstrip.  Perfect lost procedure to find out where we are.  The lost procedures are pretty easy, with the exception being night flight.  You cannot use ground references as easily as during the day time.  So VOR navigation is extremely important at night.

We continue our flight over to KAPV, but cannot really see it yet.  I queue the microphone a few times to get the lights to turn on, but we are still unable to see it.  Once out of the KVCV airspace we begin our decent, but also make sure to keep some buffer between us and the ground, since we cannot see any obstructions or mountains in our way.  We get to where the airport is, and still cannot see it.  We fly what would be a normal pattern and mike tells me he sees the runway below but still no lighting.  I’m guessing one of the lightning strikes cut the power to the airport. 

So now we have a real life diversion on our hands.  We initiate a climb up to 6500, and mike tell me we are going to cable airport KCCB, next to Ontario.  He then tunes, 122.0 for flight watch, and request a updated weather briefing, as well as inform them of the power outage at KPAV.  The weather is still looking ok over in the inland valley.  So we now are going to KCCB to get my night landings in to meet the requirements.  Once at 6500’, I pull out my sectional, AFD, and start calculating some things, as well as getting frequencies, weather, runways.  I get everything tuned in, get weather from Ontario, since KCCB does not have an ATIS/ASOS/AWOS.  We are going to be using runway 24 to land, as they are using 26 at Ontario.

From where we are currently flying we would come straight in for a landing.  So once over the mountains, into the inland valley, we begin our descent so we can stay well below Ontario’s Class C airspace.  We maintain 2500.  We stay right on the edge of Ontario’s airspace until right at Cable.  It was easy to see the airport while coming in, but I could not see the runway even with the lights on.  Once we got closer thought, the runway quickly became apparent. 

I announce the position of our aircraft while in route to the CTAF, and announce each 5 miles just about.  The first landing we were high and had a little excess airspeed.  So we floated down about half the runway before touching down.  If we would have floated any longer, I would have elected for a go around, but we still had quite a bit of runway left for stopping.  Upon landing, mike had the same feeling.  He was wondering if I was going to do a go around, but said he would have landed when I did as well.  But any further and he would have initiated a go around.  Funny how both of us fly the same and have the same reactions. 

We perform a taxi back, and take back off into the pattern.  We do another lap in the pattern, and perform a second landing.  The entire time mike and I were talking.  Not sure if that means I am a lot more comfortable now with flying to where I can talk, and not have to fully concentrate on everything I’m doing, as it’s more of a second nature now.  The second landing was much better.  I dislike KCCB as the runway has dips and humps and bumps and the airplane gets moved around a lot when landing.  It also makes braking a bit more difficult and you are in need of constant rudder adjustments to keep the plane on the runway.  We take back off and perform one more lap in the pattern.  This makes 3 landings thus far, and now landing at KVNY would make 4 and complete my requirements. 

The third landing was the best one yet, although I’m a fan of being above glideslope at night rather than below or on glide slope.  I like to give myself some extra buffer for the, what if.  We land and mike commends me for that landing, and then we take back off to come home to KVNY.  We initially climbed to 4500 to stay above other airspace, and once at KEMT we started our descent to 2500 to stay below the outer ring of Burbank at 3000’.  Contact Burbank about 5 miles out and request westbound transition to KVNY.  They vector me in for a left base for runway 16R.  Then hand me off to KVNY just before the Budweiser factory, and I get cleared to land on runway 16R.  Landing there was awesome too.  Good airspeed, good glide slope.  The airplane was flying the approach by itself without me intervening.  I set it up and didn't really touch anything except to round out and flare.


Mike liked my progress through the flight and liked how i kept within PTS limits during the hood work.  I'm suppose to do one more night flight tomorrow, and do some additional hood work so i get my requirements close to being complete.  We are also suppose to land at Burbank.  This will be my first time landing at a class c airport.  I did some reading on this, and it is practically the same thing, except i have to contact approach control and they will hand me off to tower to land.  So it's not too much different than a normal flight into a class D airspace.  Then i have my last long xcountry the Sunday after that.  Stay tuned!