Sunday, September 25, 2016

That solo write-up

I was looking for the tale Flight Training mag published...  it was archived here.

Friday, September 23, 2016

Radio and clouds

[This ended up way longer than I intended.  The takeaways are at the bottom.]

5:30 wakeup.  Receding headache.  Feeling perpetually behind trying to get out the door.  Leaking coffee cup.  A text from Mark just before I got to the airport asking my perspective on the current weather reports (decreasing visibility).  Then this overhead as I pulled into the parking lot at the airport.



But then this is what it looked like out on the ramp.  Pretty nice, eh?


The challenges didn't stop there.  iPad not properly loaded (I forgot I had re-installed a dev build of ForeFlight from scratch the night before and hadn't re-downloaded my datasets!).  Fuel tanks on the airplane nearly empty.  20 minute wait for the fuel truck.  Sprayed with fuel when testing it.

(Had this been a solo flight, I wouldn't have left the house.  But with a CFI-I on board, the margin of safety is a little farther out.)

During the preflight, we kept an eye on the sky, watching the clouds and fog.  The area around the airport was staying clear, and while there were lots of fluffies out there, we felt it was fine to continue and that we'd see if we could find a good area to practice, as long as it looked like we'd be able to get back to the airport VFR (Mark is CFI-I, of course, so worst case is that he'd have to do the return trip).

Sounds like a boatload of bad omens, doesn't it?  Perhaps that boatload was a signal of some kind, but today's flight was still worthwhile for these reasons:

1.  Radio work
2.  GPS work
3.  Seeing those conditions from (sort of) above
4.  Another takeoff/landing
5.  Interesting movements on the airport

Last night I read and rehearsed the chapters on Class C and D airspace from the book Say again, please.  (Austin-Bergstrom is C, Georgetown (where the Cirrus lives) is D.)  Jason was the controller for various contacts and I was the pilot.  It was very helpful :)

There were two goals for today's flight that were accomplished:  all necessary radio work to fly out of and into Austin and basic GPS usage.  We had also planned to do foggle work for constant airspeed climbs and descents but conditions prohibited.

Seriously, on to the radio work.  I want to replay it to help it stick in my mind.

After the preflight, we cranked up and the first call goes to clearance delivery.

Me:  "Austin clearance delivery, Cessna six five two mike alpha, VFR to the southeast training area, two thousand five hundred, with quebec."

Mark:  "I don't think they heard you.  That was the autopilot button."  Grrrrr....  I'm not used to an autopilot button on the yoke yet!  There's only ever been the mic!  I did it again with the correct button.  :)

ACD:  "2MA, Austin clearance, standby."

And a few seconds later, ACD: "2MA, maintain VFR at or below three thousand five hundred, contact departure on 127.22, squawk 2403."

Me: "Say again for 652MA."  It had come kinda quick and I was just finishing jotting down the frequency when he was done, so I missed the squawk.  In retrospect, I should have repeated what I did get and just ask him to "say squawk again, 652MA."  He repeated, half a breath more slowly, which did give me a chance to verify that I had the other info correct.

Me: "Maintain VFR at or below 3500, contact departure on 127.22, squawk 2403, 2MA."

ACD: "2MA, readback correct."

And that was that for clearance delivery.  I entered 2403 on the transponder, switched the com to ground and put the departure freq in standby, then taxied to spot 1, a huge yellow dot with a 1 in it on the ramp just before the kilo taxiway.  At this point, it was time to call Austin ground.

Me:  "Austin ground, Cessna 652MA at spot 1 with quebec."  (Repeating quebec is not really necessary, but Mark says they almost always verify that you have it at this point so adding it now saves a transmission.)

AG:  "2MA, Austin ground.  Taxi for runway one seven left via kilo bravo foxtrot."

Me:  "17L via K B F, 2MA." (Phonetic, of course.)

And with that we're off and taxiing.  Getting to any runway threshold at Austin in a 172 is a nice long straight task, so I used this time to (1) control the airplane to the right place, (2) check instruments, and (3) explore the GPS a little, with things like pulling up the KAUS page and finding frequencies.  I got my stuff in the cockpit organized and was comfortable when we pulled into the F run-up area near the threshold for 17L.

I was pretty concerned that my run-up might rock the Southwest flight taxiing behind me.  Hee hee hee.  Flight controls free and clear, instruments good, 1800 RPM, gauge checks, mag checks, annunciator checks, set everything for take off and taxi to the line.  Now to talk to tower.  If I had really thought through the order for accessing frequencies, I would have put tower in the standby instead of departure, so I took a sec to get set up with tower active and departure on standby.

Me:  "Austin tower, Cessna 652MA, ready to go, 17L."  This seemed awkward, or too casual or something.  It's stuck in my head.  Say again, please gives an example with "ready for takeoff on 17L" which is much more precise.

AT: "2MA, Austin tower, standby."

(This next part of my memory of the exchange is a little fuzzy.  I was thinking it happened before we started the taxi, but the offer of help wouldn't have come from ground. It basically went like this...)

AT:  "2MA, conditions in the southeast training area are not favorable for VFR.  If you get up there and decide to come back, let me know and you can stay in the pattern."

Me:  "Roger, thanks, 2MA."

At this point, we were accepting that it was a real possibility that we'd get up there and not leave the pattern, but would at least go for that.

AT:  "2MA, Citation on 9 mile final, line up and wait on 17L."

Me:  "Line up and wait, 17L, 2MA."

That cleared us onto the runway but did NOT clear us to takeoff.  I taxied onto the runway and turned to line up on the centerline, moving as little as possible down the runway so that if/when that Citation came overhead, they'd have plenty of room past us.  But 9 miles was pretty far away, and just as I brought us to a stop....

AT:  "2MA, cleared for takeoff, 17L, fly heading one three zero."  He might have said "cleared to depart" but the message is the same.

Me:  "Cleared for takeoff, 17L, will fly heading of 130, 2MA."  (Whatever he said to me is what I would have said back.)

Full throttle, right rudder, airspeed is alive, gauges in the green, rotate, fly runway heading while accelerating, around 500 feet turn left to 130.  A moment later, ....

AT:  "2MA, contact Austin departure. Good day."

Me:  "Going to departure, 2MA. Good day."

This is a perfect illustration of anticipating what comes next.  We knew departure was next, so it was loaded into the com and required pressing one button to swap to the active frequency.  This was easily done while climbing and assessing the clouds that we were immediately faced with.  Aviate, navigate, communicate.

Me:  "Austin departure, Cessna 652MA, one thousand eight hundred."

AD:  2MA, Austin departure, radar contact, squawk [something different]."

Me:  "Squawk [whatever], 2MA." I didn't write that one down, just punched it in.

It is entirely possible at that time that we were only 800', which would be an incredible mistake on my part to have said 1800'.  From takeoff to talking to departure to (next) changing heading to maintain VFR to calling it off happened within the span of a couple minutes and we maxed out at 1800', comfortably below the clouds above, comfortably above the fog below, but with no great openings in sight.  There was a big heavy blob of cloud hanging a little lower in front of us, so Mark quickly called departure and asked to turn left ten degrees to maintain VFR, and the departure controller responded that the heading change was approved.

Mark and I chatted for a minute about our options and he left it to me, as PIC, to make the call.  While I really loved the unique sandwich we were in, I did not (1) see a way to perform maneuvers safely nearby, (2) see a way to unequivocally stay VFR to get to somewhere to perform maneuvers, or (3) have faith that the terminal area would stay clear over the next hour.  So I called it off.  With that decision, I immediately called departure back.

Me:  "Austin departure, 2MA would like to return to the airport because of conditions for full stop."  Ordinarily you'd say your position relative to the airport, but I think we were only 6 nm away, were still well within the outer ring, and had only just talked to them (plus it wasn't crazy busy this morning) so it seemed very likely that we'd be on his radar, hardee har har.  Had we been farther out, we would have been calling Austin approach.

AD:  "2MA, expect left base, runway 17L."

Me:  "Expect left base, 17L, 2MA."

We were far enough away and there was enough fog that I couldn't pick out the airport or even the buildings in downtown.  Hey!  I can use the GPS!  It was on the airport page for KAUS, so I punched the direct-to button and viola!  Heading to the (center of the) airport.  Once I was on heading, I knew I'd need to stay right of that to set up on left base so I focused on maintaining altitude while trying to pick out landmarks.  Finally it appeared.

AD:  "2MA, contact tower on one two one point zero."

Me: "Going to tower on 121.0, 2MA."

[Switching frequencies...]

Me:  "Austin tower, 652MA, one thousand five hundred." Or similar altitude. :)

AT:  "2MA, Austin tower, enter left base, cleared to land runway 17L."

Me: "Left base for 17L, cleared to land, 2MA."

There were a few wispy fog-clouds in the pattern, but we stayed clear.  I did a fair job of reducing power, slowing, and putting in flaps as we approached base, like unwinding the pattern.  I landed us a little long thanks to trying to round out the descent and turning it into an early flare accidentally, but it was fine.

AT:  "2MA, taxi on 17L to kilo, then contact ground."  This was unexpected, since we could easily have turned off at juliet, though kilo is the straight path back to the FBO.

Me: "Will taxi to kilo then go to ground, 2MA."  Mark put the ground frequency into standby.  After turning off at kilo and just clearing the runway threshold, Mark prompted me with the call to make.

Me:  "Austin ground, 652MA heading to Atlantic." This is another bit that stuck in my brain as wrong.  Heading means that number you dial into the DG, not "I'm going to [location]."  Stupid!  Mark's prompt didn't say "heading to," to I'm not sure why it rolled out of my mouth.

AG: "2MA, Austin ground, taxi to Atlantic."

Me: "Taxiing to Atlantic, 2MA." And thus ended the radio work.  Taxi was normal, shutdown was normal except that the checklist doesn't say to turn off the avionics master before pulling the mixture and I forgot to install the control lock but luckily Mark remembered.



The end.  Two hours later at work it was overcast and raining.  Two hours after that it was partly cloudy and humid as all get out.

-----------------------------------

The takeaways:

Every frequency has a discrete purpose.  Sometimes the same person will handle several frequencies, but they all each have a purpose and there's an order to calling them.  These notes are specifically about Class C.  D is simpler.

1.  ATIS.  The first frequency is just for receiving terminal weather and information, such as taxiways that are closed, bird activity in the area, etc.  Zoom out to...

2.  Clearance delivery.  If you're opening an IFR flight plan you'll get that from clearance delivery.  If you're in Class C, you have to be cleared to use the airspace.  For VFR, this means giving them a heads-up for what you want to do and getting a transponder code (so they can track you) and permission.  Zoom out to...

3.  Ground.  Ground controls all aircraft in the movement area.  You can taxi around the ramp all you want without talking to anyone, but (for departure) to cross into a taxiway or runway you need permission from ground.  After landing as soon as you get off the runway, you need to stop and talk to ground about your movements.  They're the eye on the airport coordinating ground traffic -- including aircraft, trucks, mowers, and so forth.  They have jurisdiction from the ramp to the runway threshold.  Zoom out to...

4.  Tower.  Tower is in charge of the runway and taxiways between runways.  They sequence aircraft for spacing and choreograph takeoffs and landings.  As soon as you're on your way and safely on the heading they give you for departure, they hand you off to departure.  Zoom out to...

5.  Departure:  This is the eye in the sky that helps get you through the Class C airspace in the direction you want to go.  They control outbound aircraft in the ring spanning 10-20 nm from the airport center.   Zoom out to...

6.  Center:  We haven't talked to center for these local VFR flights, but on an IFR flight you're constantly someone's responsibility, and after departure it's center.  Sometimes you go to other approach controllers along the way, but center helps out with big regions.  Max zoom achieved!  Zoom in to....

7.  Approach:  The opposite of departure, they control inbound or transitioning aircraft within the ring.  Zoom in to...

8.  Tower.  Zoom in to...

9.  Ground.  Zoom in to...

10.  UNICOM.  Maybe you need to call for fuel or a car.  This is basically just a local call to the FBO/GA terminal for non-flight assistance.

The other takeaway is that there's a pattern.  Up until flying the past two weeks out of Austin, I've only ever used CTAF (except the two requisite towered-field ops during PPL training ten years ago), which I can do with great ease.  These different frequencies and how to talk have seemed very cryptic, but not only does each have a purpose (that greatly narrows what you say and why), there's also a pattern!  Generally speaking, "who, who, where, what."  Just like CTAF.  Sometimes you leave parts out.  Sometimes you end with the information identifier.  But generally speaking, that's how you generally speak.  Now that I get that, it'll be easier to become proficient.  Whew.

Monday, September 12, 2016

Almost refreshed...

Here we are, halfway through September of 2016, and I'm starting to fly again!


This morning my CFI for the upcoming instrument training, Mark Lush, fellow ForeFlighter, and I went up for a second refresher flight.  The intention was to knock off some more dust.  We got in a set of steep turns, which were better and easier than last week's pair, and did three touch-and-gos at Smithville (84R) before returning to Austin-Bergstrom where Above & Beyond Aviation is based.

My pattern work was much more finely tuned this time, and I made all the radio calls at Smithville (felt totally natural), coordinating with the other KAUS-based trainer that was also doing touch-and-gos at 84R.  My flares were kind of all over the place today; one was far too high (resulting in a hard touchdown), and one had a big ballooning that I haven't figured out yet other than too much backpressure at the wrong time.

I felt I had more mental cycles today, enough to actually open ForeFlight and use it get back to KAUS for a left base for 17L.

For the next flight (hopefully Wednesday morning), we're going to stay closer to Austin and do the last flight review maneuvers to sign me off for solo VFR flights again -- slow flight, stalls, maybe turns around a point.  Wish us calm winds for Wednesday!

Next week we'll start instrument training.


Wednesday, October 09, 2013

Weather, navigation, and maneuvers. Take a deep breath.

Weather review was pretty straight-forward.  I may not remember the name of exactly which graphical weather product to go to for any specific item, but I'm confident I can find it during preflight in ForeFlight or online.

Navigation was easier than expected.  I actually remembered VOR navigation, which is the only type I was a little anxious about.  Other than GPS and pilotage, that's what I'd use.  I didn't bother reviewing the NDB nav process, and hopefully that won't come back to bite me in the keister.

Maneuvers made me a little anxious.  Mentally, mostly, I've got it.  When you're in the plane, though, it has to be(come) natural with muscle-memory and innate feel and reactions.  It's just a lot to try to visualize and anticipate all at once.  The first time around, this stuff was all spread out over a few months.  I'm interested to see how much feeling comes back in that first flight.  It helps to have flown with Jas during the past years, but being PIC will be a different story.

I have my first flight scheduled for Friday morning.  It's a 1982 Cessna 172P (just downloaded the POH) with at least one Garmin 430.  The instructor scheduled us in the plane for 2 hours and another hour on the ground.  I'm hoping we can do the BFR in this time, but it all depends on the return of the feeling and competence, at least enough to continue solo PIC for practice, calling in Jas or the instructor as needed.

I'm also happy to be doing it during autumn -- beautiful, crisp days with less turbulence, so less distraction from learning!

Monday, October 07, 2013

Charts, airspaces, communications, information...

This stuff is coming back pretty quickly...  yay!  I do have to say, though, that a lot has changed since I first became a certificated private pilot.  Yes, reading paper charts is a necessary fundamental for safe flying and navigation.  But in the interceding years since last I sat left seat, I've be right seat, an armchair pilot, and a developer for ForeFlight.  Digital tools like ForeFlight make it so easy to find out what you need to know.

For instance, one of the things I didn't remember was that the ticks coming out from an airport icon on a chart mean that during business hours, the airport offers services and fuel.  Nowadays, I wouldn't look at a sectional to find that out; I'd see the airport on the sectional in ForeFlight and tap it to find out its details, including when it operates, whether it offers fuel (self-serve or by lineman), and so many other things from current METAR to frequencies to airport elevation and pattern altitude and so forth.

I'm not starting a discussion about digital v. paper.  All I'm saying is that the information is easily and quickly available at a tap on the iPad.  Barring device failure.  And backup device failure.  :)

Another thing to say about my approach to flying is that I'm a planner.  I like to thoroughly debrief every spot along the projected path, all airports along the way, and really try to minimize surprises.  That's probably the way of most student and low-time pilots like myself; but the killing zone is on the horizon, and that, I imagine, comes partly from complacency about these kinds of details.

Moving on...  Airspaces.  Almost everywhere I've ever flown has been Class E, like my primary training homebase of KJGG and now KUZA, or Class D (towered with no radar services), like KPHF.  KUZA is a little more interesting since it's under one of Charlotte's Class B shelves.  This means from the surface up to 3600' MSL we're in Class E and can fly under VFR rules and choose our own destinies.  Once we go above 3600', or head into an inner ring of Charlotte airspace where the floors of the Class B shelves are lower, we must already be in contact with ATC, must have a Mode C transponder (reporting altitude and assigned code), and must follow their directions.

The main thing that's important to VFR pilots are the environmental rules.  To participate in a VFR flight, you have to be able to see, and the minimum requirements are 3 statute miles of visibility (think low haze) and the ability to stay clear of clouds by at least 500 feet below, 1000 feet above, and 2000 feet horizontally.  For safety.

Class B airspace is reserved for mega busy airports, like Chicago and Atlanta.  Class A is used between 18000' MSL up to 60000' MSL (FL180-FL600) and requires an IFR flight plan.  Above that, it goes back to Class E, but you usually only find space-faring vehicles there....

There's also a Class G airspace, but that's rare, except to bush pilots in Alaska.  The rules there are fewer yet, and almost boil down to common sense.  (Update: I think I'm wrong here; abundance of airports just makes it more practical to treat non-controlled airspace on the east coast as all Class E.)

Special airspaces, MOAs, restricted airspaces, ADIZs, ...  all on the charts.  TFRs change airspaces periodically and must be verified before takeoff.  NOTAMs should also be consulted before takeoff, but usually pertain to non-standard airport operations (equipment that's offline, change in traffic pattern, scheduled event altering landing availability, etc).

Moving on....  Communicating.  The transponder is what allows radars to find an aircraft.  The radar pings, and the transponder responds.  Mode C transponders report both the squawk code and altitude, and are required to interact with ATC.  When flying VFR (without flight following), the transponder is set to the VFR code of 1200.  The transponder will still respond to pings, but ATC will only know that there's somebody out there at that location and altitude; this is helpful for advising any pilot of traffic (you!).  Though transponders are nearly ubiquitous, they are not required for VFR operations and so traffic may be out there that ATC can't see and that your in-cockpit traffic advisor (traffic scope, ADS-B) can't alert about.  That alone underscores the importance of a VFR pilot maintaining situational awareness and keeping a good scan going.

Other important squawk codes are 7500 (hijack), 7600 (lost communications), and 7700 (mayday).  When dialing in a code, it's important to be mindful that these aren't entered accidentally, even for a moment.

Radio communications should be brief, concise and professional.  CTAF (common traffic advisory frequency) is published for each non-towered airport, or towered airports when unattended, and is how aircraft in the area coordinate and avoid each other; it's also usually the frequency the pilot would use to activate pilot-controlled lighting for night operations.  UNICOM, sometimes the same as CTAF, allows the pilot to talk to someone at the airport for advisories, to request fuel, etc.

Lots of times, the same frequency is used at multiple airports and you'll hear transmissions that are irrelevant.  It's important to (1) listen for the location of the other transmissions and (2) remember to include yours.  The standard flow for self-announcing via CTAF is "Audience, identification, message (frequently location and intention), audience."  For instance, "Rock Hill traffic, Cessna 4321A, 10 miles southwest of the airport inbound for landing runway 20, other traffic please advise, Rock Hill."  Proper radio usage also means not "stepping on" other transmissions; only one person should be speaking at a time, so wait until the freq is clear before starting your transmission.

When talking with ATC, you typically hail them and state your identification, then wait for them to get back to you.  There's a good chance they're managing other aircraft and may be busy at the moment.  "Charlotte approach, Cessna 4321A."  This applies at towered airports as well.  You need to engage the controller before starting the conversation.  This gets a lot more important when flying IFR, so I'm not going to dwell on it here.  Also, the flying I expect to do in the near term will not use this, so I'll get more detailed when the time comes.

In case of lost communications, there are some basic troubleshooting steps to take, like verifying the frequency, checking that the headset is plugged in, and trying the alternate transceiver (radio).  If all else fails, squawk 7600 and be extra vigilant.  For landing in Class D airspace, you'll need to watch the tower for light signals -- this is a good time to reference the signal legend you have on your kneeboard or in ForeFlight.

7700 on the transponder usually goes with 121.5 on the radio (although if already interacting with ATC you'll probably keep these comm settings as they are unless instructed otherwise).  121.5 is the mayday frequency.  Distress signals are started with "MAYDAY, MAYDAY, MAYDAY."  Urgent situations start with "PAN-PAN, PAN-PAN, PAN-PAN."  The aircraft's ELT (emergency locator transmitter) also broadcasts on 121.5 automatically upon impact.  The freq should be checked periodically to make sure your ELT isn't sending false alarms, and there are procedures governing testing the ELT.

Moving on...  Information.  A/FD.  FAR/AIM.  NOTAMs.  ACs.  If not getting it from ForeFlight, faa.gov would be my next resource, especially for NOTAMs and TFRs, and in the air an FSS or UNICOM can be consulted for up-to-date advisories.

Next:  Weather!  (Thanks to intermittent work with ForeFlight, this part should be quick.)  Aircraft performance and weight and balance.  Navigation.

Wednesday, October 02, 2013

Approaching a stall, maneuvering in flight

The next few textbook sections covered basic forces of flight, control surfaces, center of gravity, aircraft stability, and here we are at stalls.

A stall happens when the wing can no longer produce enough lift to support the aircraft.  The reference point for this condition is called the critical angle of attack.  It can happen in various situations, but the clearest to consider is the climb, when the wings are inclined and the air flowing over the wings is less.  You can easily envision a breaking point when the airflow around the wing is just messy, and that's the stall point.  We talk about it as stall speed, because the cockpit instrument that measures the airflow over the wing is the airspeed indicator, and the airflow needs to be at least VS1 (or VS0 with flaps out) to keep from stalling the wing.

The stall speed can change.  More weight, loading the airplane with a CG too far forward, and the presence of ice or other irregularities on the wing can increase the stall speed.  Use of flaps decreases the stall speed, allowing slower controlled flight.

Two main types of stalls are practiced during flight training:  power-on and power-off.  A power-on stall happens when you typically have the throttle in, such as during take-off or a climb.  Stalls during this phase of flight when lift is disrupted due to a too-high angle of attack (nose too high) or retracting the flaps too early.  Power-off stalls happen when the throttle is out, such as during landing, and are actually desired to be the last thing to happen as you touch down -- you've "bled off" all the speed you can, stall and settle the last inch onto the runway.

No matter the type or reason for the stall, the recovery process is the same:  nose down and power in.  As the airflow over the control surfaces is quickly restored, return to straight-and-level flight and adjust the throttle to an appropriate setting.

Stalls usually give me sweaty palms.  I can totally deal with the concepts involved, and in practice I have recovered them and used them upon landing to my advantage.  However, it's the potential for an unrecovered stall to progress into a spin that freaks me out.  So I suppose that spins give me the sweaty palms, but stalling is the first step in spinning!  General recovery process (check POH for detailed recovery):  power out, neutral ailerons, opposite rudder, return to straight-and-level flight.  At a typical loss of 500 ft per turn, and a turn happening in just 3 seconds, there's no time to consult an emergency checklist.

Okay, moving on to maneuvers.  Climb, descend, turn.  Points to remember:

When climbing, the aircraft tends to turn left slightly due to things like engine torque and asymmetrical thrust produced by the twist of the propellor blades meeting the angle of attack.  Slight right rudder is used to maintain a straight flight path.

When descending without power, glide speed and angle are preeeeeetty important.  The POH will indicate the best glide speed for the aircraft.  Upon engine out, the first thing on the checklist is to trim for best glide speed (then troubleshoot); this will keep you in the air the longest while you attempt a restart or select a landing site.  Best glide speed can be affected by wind, so for once you'd be looking to land with the wind.

When turning, pay attention to load factor.  The increased Gs on the wings decreases lift and increases stall speed.  To maintain altitude, some back pressure will be needed.  Load factor that goes too high can damage the structure; for the normal category aircraft we fly, they're limited to 3.8 positive Gs and 1.52 negative.  Also relevant here is the maximum maneuvering speed (VA) published in the POH; it's the max speed at which abrupt control inputs or turbulence can be tolerated by the airplane.

That wraps up the fundamentals of flight.  Next up are the practical matters of reading charts and understanding airspaces, followed by radio communications, weather, navigation and flight planning.  These next parts should go quickly, thanks to continue to fly with Jas and being involved with ForeFlight....

Gyroscopic instruments

The turn coordinator, attitude indicator (artificial horizon) and heading indicator are based on gyroscopes.  Gyroscopes have spinning wheels that maintain their position as their anchoring hardware moves around them.  These wheels require some sort of power to spin; the turn coordinator is typically electric, while the other two are vacuum powered.  I don't think I ever wondered "why vacuum?" before, but you can probably guess that I did today!

There's either a vacuum force created by design of the system, or a vacuum pump within the system, for these instruments.  It sucks air from the intake, through a filter, through tubes and instruments, through a pressure release valve, and then exhausts it.  The book doesn't have a diagram, but I'm imagining fins on the gyro wheel to catch the air, like on a water wheel for catching water.  As long as the air is flowing, the wheels will be spinning.

Because of precession, or the introduction of error in gyro-based readings due to friction, gyro instruments must be periodically cross-checked and/or recalibrated.  Most notorious is the heading indicator, also called the directional gyro or DG, which should be compared to the whiskey compass (magnetic) every 15 minutes or so.  The whiskey compass, however, gives temporarily inaccurate readings while turning, accelerating or decelerating and is affected by turbulence as well.

Another direction-relevant complication is variance, or the difference between true north and magnetic north.  Instruments are set relative to a magnetic reading, yet charts and publications use a true north reference.  Since the magnetic field of the Earth changes from place to place, it's important to know the variance at your location.  To give you an idea, the variance along the east coast ranges from roughly 0 degrees west to around 20!

Monday, September 30, 2013

Pitot-static system

The pitot tube generally hangs from the wing with the opening forward and positioned forward of the area where air becomes displaced by the wing.  This device senses pitot (or ram) pressure and is used by the airspeed indicator.  The pitot tube has a drain at the back to release any moisture from the air that may otherwise accumulate and affect the readings.  Where there's moisture, there's the potential for ice, and so the pitot tube is equipped with a heater that can be activated from the cockpit.  How do you know when there's ice (or another blockage), though?  That depends...

If the pitot intake is blocked, but the drain is still open, then the air already in the system will have a path to escape, resulting in a gradual reduction in pressure.  Lower pressure is usually a sign of less air being forced into the pitot tube, so the airspeed indicator will show a slower speed.

If the pitot intake and drain are both blocked, or if there's a block between the pitot tube and the instruments, then the air in the system is trapped and the pressure will remain constant.  With no changes in altitude or atmospheric pressure, the airspeed indicator would remain unchanged, and so the pilot may not suspect a problem.

A problem will become evident, however, as altitude changes.  Generally, airspeed decreases during a climb and increases during descent.  The airspeed indicator uses not only the ram pressure but also the static (ambient) pressure to determine airspeed; basically, the static pressure fills an area of the instrument, and the ram pressure tries to inflate something within the area -- less inflation means slower speed.  (Incidentally, an airplane with higher groundspeed at a higher altitude can show the same indicated airspeed as an airplane with lower groundspeed at lower altitude, thanks to air density.)  So imagine that the airplane is indicating 140 knots when the static pressure increases, say upon descent.  Increased static pressure with constant ram pressure will cause the device to deflate a bit, which will result in lower indicated airspeed, which is typical of a climb.  This observation should raise a red flag.

The static pressure is sampled by a static port, mounted usually along the fuselage and in such a way that it just senses the ambient air pressure.  Air pressure is measured in inches of mercury (" Hg), standard of 29.92" Hg at 0 MSL, and broadcast as part of the METAR for local airfields.  As part of preflight, you hop in the plane, tune in the local AWOS or ATIS, and dial the current barometric reading into the altimeter.  In fact, they announce it as "altimeter 3-0-0-1."  If all goes well, adjusting the barometer will result in an altimeter reading that matches the airport's altitude above sea level.

When the static port gets clogged, that affects the airspeed indicator, the altimeter and the vertical speed indicator (VSI).  The altimeter will just get stuck since the pressure is trapped inside.  The VSI will get stuck at 0 since it registers changes, and no changes will occur.  The airspeed indicator, though, will give incorrect measurements.  Typically the static pressure and ram pressure are "in sync," so to speak -- high pressure means high air density in the chamber and lots of air molecules funneling through the pitot tube into the inflatable portion of the airspeed indicator; low pressure means low air density in the chamber and fewer air molecules to be rammed.  When the static port is blocked, the static pressure is held constant regardless of outside air pressure, so it's no longer coordinated with the ram pressure.  Say it gets blocked at 3000' (that is, at a specific air pressure).  On a normal climb from here, the ram pressure would be decreasing and so would the static pressure, but now the ram pressure will decrease but the static pressure will not, resulting in slower than usual indicated airspeed readings.  On a normal descent from 3000', the ram pressure would increase and so would the static pressure, but in this case only the ram pressure will increase and the airspeed indicator will read faster than expected.

Those are considerations when there's a malfunction of some sort.  Pilots also need to consider what happens just when moving from region to region when the air pressure changes.  The saying goes "High to low, look out below."  Let's dissect that.  Your altimeter is set for a barometer of 30.01" Hg as Charlotte Approach just gave you.  In the vicinity of Charlotte, you'd expect your altimeter to be fairly accurate.  Flying at 2600', you head west toward the mountains, where the pressure is dropping.  The standard conversion is 1" of mercury for every 1000' of altitude.  If you don't adjust your altimeter and try to maintain your 2600' of indicated altitude as you fly into an area with a pressure of just 29.01" Hg, your true altitude is now just 1600' -- look out below!  As the terrain comes up, you really don't want to be going down.  Lower pressure means less dense, which under standard conditions means higher altitude; under non-standard conditions it means update your altimeter!

That's it for today.  I started off today with Rod Machado's Private Pilot Handbook.  It is so dreadfully corny, and way too distracting for me to use as a serious refresher aid.  Sigh.  I like my old Guided Flight Discovery textbook, but in places it's just so flat.  I also did an experiment today and decided to study from home instead of at the library.  That just doesn't work!  My focus was definitely less honed.  The dishwasher needs unloading, the laundry needs folding, there's a bug on the window, a lizard just crawled up the deck railing, the cat wants to be petted, there's that new "green monster" smoothie recipe I was thinking of trying, the Keurig needs more water, ....  Back to the library on Wednesday.  With one of these tasty new smoothies.