The mysterious "third engine" of the CRJ-900.

If you look closely at commercial aircraft, you might notice something that looks a bit like an extra engine. Consider the CRJ-900 for example. It clearly has only two engines, but take a look at the tail. It has an additional jetpipe which surely resembles a third engine.

So what’s the deal? Hold onto your butts: it is a third engine. In fact, it’s a very special kind of engine found on airliners and some corporate jets called an Auxiliary Power Unit, or APU.

The APU is an internal and highly automated powerplant that provides backup power to a number of systems and provides pressurized air for main engine starting.

As you aviation-savvy readers already know, redundancy is the name of the game, and an APU provides plenty. A typical APU spins an electrical generator that is capable of providing electrical power to most (or all) onboard systems in the event of a dual engine or primary generator failure.

Furthermore, bleed air is pulled off the APU’s compressor to provide hot pressurized air for use in air conditioning and pressurization systems.

The APU exhaust of an Air Canada ERJ-190

Under normal circumstances, APU’s are used by flight crews to aid in engine starting and to provide air conditioning for passenger (and crew!) comfort on the ground. Typically, the APU will be shut down at some time before takeoff or as part of the climb checklist, effectively transferring all electrical and air conditioning systems to the main engines.

In the interest of safety, APU’s are heavily isolated in modern aircraft. For example, on my aircraft (the CRJ-200), the APU is enclosed in a fireproof titanium box and features its own semi-automated fire detection and fire extinguishing systems, completely separate from other aircraft systems. In theory, the APU could burn itself to a cinder without endangering the passengers or crew, which is a comforting thought.

You can read more about APU’s at Wikipedia.

Patrick Flannigan is a regional airline pilot and aviation blogger. You can read more of Patrick’s articles at AviationChatter.com.

Do you know your airplane's MPG?

“What is meant by the term ’specific range’?”

This is the question that I asked David Wyndam of Conklin and de Decker after coming across this term while looking at some aircraft comparison performance tables.

The performance tables listed the specific range for various airplanes in both long range and high speed cruise.  For instance, the specific range for a Cirrus SR22 was listed as 2.051 for long range cruise and 1.810 for high speed cruise.  But what exactly do those numbers mean and what formula was used to devise those values ?

Specific range is the distance an aircraft travels per unit of fuel consumed. Typically this is expressed in nautical mile per pound of fuel.  So for instance, the Cirrus SR22 has a high speed cruise specific range of 1.890.  That means for every pound of fuel used, the Cirrus SR22 could fly 1.890 nautical miles.   Here is another example.  The Beechcraft Premier that I fly has a SFC of 0.557 NM/lb.   If 1 lb will take me 0.557 NM that means with 1,000 lbs of fuel the Premier can fly 557 NM.  This is the aviation equivalent of MPG.

One purpose of SFC is to help determine the efficiency of an aircraft.  This can be used when comparing aircraft for purchase.  Fuel efficiency is important for knowing what your direct operating costs will be as fuel is one of the largest components of DOC.

Now we don’t typically use pounds for the fuel unit in piston aircraft, we use gallons.  We also know that 1 gallon of 100LL weighs approximately 6 pounds.  So if the Cirrus can go 1.890 nautical miles on 1 lb, that mean on 6 lbs (or 1 gallon) the Cirrus can fly 11.34 NM.   On 60 lbs, or 10 gallons, the Cirrus SR22 at high speed cruise can fly 113.4 NM.  Here is the high speed specific range cruise figures (and some corresponding ranges)  for 3 different single-engine piston aircraft:

To find the values in the lower row I took the specific ranges values and multiplied them times 60 to find the range on 10 gallons of fuel.  Here is a map with range rings representing those values:

How far can you go on 10 gallons?

So how can you figure the specific range (SFC) for your aicraft?  It’s actually quite simple.  Just take your TAS (true airspeed) and divide it by your fuel flow in pounds.  So, let’s say your TAS is 130 knots and you are burning 11 gallons  an  hour (or 66 pounds an hour):That is a specific range of 1.969.  On 10 gallons of fuel, this airplane could fly 118 nautical miles.

So is the higher SFC number always the more efficient airplane?  Not always.  For instance, the Boeing 737 has a long range SFC of 0.090 and a CJ3 has a SFC of 0.606.  But, if  a 737 can carry 135 people and the CJ3 can only carry 7, which aicraft is really the more efficient airplane?  There are many other factors to include in efficiency comparisons as well such as fixed and non-fixed maintenance costs.

Thanks again to Conklin and de Decker for their helpful input to this post.  If you are looking for professional aicraft comparison software or handbooks, Conklin and de Decker have a wide range of products for a wide variety of aircraft both single engine, jet and rotorcraft .

A common problem that I see in many of my students (both primary and advanced) is the failure to adequately brief the takeoff and departure segments.  This is a critical and common mistake with many pilots.  Richard C. Cushing summarized the importance of planning when he said:

Always plan ahead. It wasn’t raining when Noah built the ark.

This quotation really summarizes the purpose of a good takeoff briefing.  A takeoff briefing should clearly state your plan-of-action for both when everything goes as planned and “when it starts to rain”.    Because as the proverb says:

He who fails to plan, plans to fail

So then, what should you include in a takeoff briefing?  I think a good takeoff briefing is one that answers questions. Questions like:

• Who will perform the takeoff? Student or Instructor?
• Which runway are you departing?
• What type of takeoff is going to be performed? Normal, rolling, short field, soft?
• What will I do if I lose an engine during the takeoff roll? What about a engine loss at 50 feet? 500 feet?
• What are the critical V speeds for this particular aircraft? Vx, Vy and Best Glide.
• What are the departure instructions? Is there an obstacle departure procedure that I need to be aware of? Does my departure clearance include a SID?
• Which airport would I go in case of an emergency and the airplane was still flyable?  Sometimes the departure airport isn’t prepared to handle an engine fire or has a runway long enough to deal with a complete hydraulic failure.

Do you see now the importance of including a pretakeoff briefing before each and every flight? This is not a procedure just for the first-flight-of-the-day.  A takeoff briefing should be performed if you’re staying in the pattern, departing on a cross-country and with or without an instructor present.  Every takeoff is unique and each requires a different course in the case of a malfunction.  It should also be noted that a verbal (as in out-loud) briefing should be performed in both single pilot and crew pilot configurations.  Just because you don’t have a pilot sitting in the cockpit listening to you doesn’t make the exercise without merit.  Verbalizing and listening to your own voice through the intercom / headset is a good way to solidify and commit your intentions to memory.

Here is a a sample takeoff briefing that I would use in a single-engine aircraft:

This will be a normal takeoff.  We will departing on runway 24 with an initial altitude of 3,000.  Vr is 50 and Vy is 67.  If we have any problems before rotation or with adequate runway remaining after liftoff, we will abort.  Standard emergency procedures will be used in the event of engine failure without adequate runway remaining.  Best glide is 65 KIAS.  We won’t even think about returning to this airport unless we are at 1,000 AGL.  Any questions or comments?

As you graduate into more advanced aircraft, you’ll notice that your takeoff briefing will have to be adapted to match the performance of that airplane.  For instance, here is a sample takeoff briefing for a light jet aircraft:

This will be a rolling takeoff with flaps set at 10 from runway 23.  We will abort for any reason below 80 knots.  After 80 knots we will only abort for engine fire, engine failure or  failure to maintain directional control.  After v1 we’ll handle it as a in-flight emergency and continue the takeoff roll.  Memory items will be as required and hold all checklists till 1,000′ AGL.   If we have to return, we’ll request a left downwind for 23 and pattern altitude is 1,500′. Departure instructions are the Airport 5 SID which has us making a left turn to 210 deg at 500 feet.  Standard calls. Any questions?

I’ve provided these as a basis for you to develop your takeoff briefings.  I’ve warned you about the dangers of not using a pretakeoff clearance but there is also a danger in “rote” recitation where you can just say the words, without really giving them the thought they deserve.

I don’t have to rehash the accident statistic rates here, but I’m sure you know how a large majority of aviation accidents and incidents occur during takeoff and landing phase.  That is why it is so crucial that we plan for a emergency before they happen.  Playing defense against an emergency, without a clear cut plan, is much harder than playing an offensive maneuver that has been rehearsed and discussed.

Fly Safe (and brief those takeoffs!)

Lightspeed Zulu

This was the underdog product that had the most to prove in my battle of-the-headsets.  I’ve heard some glowing reviews about them from my pilot friends and wanted to see…I’m sorry, hear the proof for myself.  I decided to purchase a pair from MyPilotStore.com for$850 with free shipping.  I couldn’t wait to try them out.

Lightspeed Aviation Zulu from MyPilotStore.com

The Zulu’s arrived a couple days later and the first thing I noticed about them was the weight (13.9 oz.) They seemed very light and well made; not flimsy, just solidly built. Turns out the reason for the light weight is the  construction from stainless steel and 4 different type of composite plastics.  Take the ear cups for example, which I learned later are made from magnesium.  The magnesium gives the Zulu’s earcups plenty of rigidity and makes for an excellent sound barrier which means even when moving around the cockpit or turning your head, your going to keep the noise out.  The other thing I noticed about the headset when it arrived was  Zulu’s controller.  I noticed the controller had some extra buttons that I wasn’t familiar with, but I’ll get to that in a second.

The Zulu trial:

My first flight using them was in the Beechcraft Premier, which has quite a bit of blower noise in the cockpit.  I typically put on my headsets right after the engine start and I noticed almost immediately (very comfortable by the way) that the passive noise reduction was very impressive.  Even with no ANR (active noise reduction) turned on, the headsets were very very quiet. I did turn the ANR on (the light (A) starts blinking green) and it suddenly got VERY quiet up front.  I could tell it was noticeably quieter than the Bose. Almost too quiet (I kind of like a little engine noise…I get a little nervous when I think the engines have stopped).

I was told by another Zulu owner that one feature I had to try out was the bluetooth connectivity feature.  Bluetooth is a type of short-range wireless network that allows other Bluetooth equipped devices to share information and data.  For example, my phone (the Blackberry Storm) is a bluetooth enabled cell phone.  I can actually link the Lightspeed Zulu’s to my Blackberry Storm and use the Lightspeed Zulu as a handsfree device! It didn’t take me too long to figure out this feature either.  You simply hold down the bluetooth button (F) on the Zulu’s controller for 5 secs (it will flash blue /red) and then set-up your phone to connect  (or “pair”).  It takes a couple seconds to find your phone and you might have to click “allow” on your BB Storm to confirm the bluetooth connection.  But once connected, there are a couple of neat things you can do, like:

• Press the Bluetooth button (F) on the Lightspeed’s controller once for voice dialing (if supported by your phone).
• Press the Bluetooth button once to answer the phone when it rings.
• Press the Bluetooth button once to disconnect from a call.
• Press and hold the Bluetooth button for 2 seconds to redial the last number called. Use the Bluetooth volume buttons (Zulu’s + and - buttons {H}) to adjust volume.

Once I tried out these features, I had an idea:  What would the Zulu’s controller do if I put my Storm in media player mode? Turns out, now Zulu’s controller acts as a music player remote control!  I can play, stop and adjust the volume on the Storm’s media player.  And as I was listening to the music, I pushed another button (D) on the Lightspeed’s controller, “FRC”.  FRC stands for Front Rear Channel and it is simply an amazing audio feature.  Headsets are notoriously awful for recreating true stereo.  Stereo music is designed to be listened through stereo speakers not headsets.  I’m not an audiophile, but apparently it has to do with the way that music is mixed in the studio, it is not designed for headsets.  All I know, is that when I pushed the “FRC” button on the Lightspeed controller, I thought I had suddenly slipped on a pair of audiophile quality headphones, not a pair of aviation headsets.  The sound quality was absolutely stunning.  In fact, I called up one of my passengers to try it out for himself.  I had him put on the headsets while it was not in FRC mode and then I pushed the FRC button while some music was playing (streaming via bluetooth from my Storm) and he was quite impressed.  He said, “Sounds like a pair of expensive home audio headsets”.   The other neat thing about listening to music while flying was the Auto MusicMute feature which dims the music volume by 80% when radio communications come in from the panel.  That way you don’t miss any important radio calls, but the music stays low enough to hear it in the background.

My only complaint about the Lightspeed Zulus (and it’s kind of a big one) was the clamping force.  After a couple other flights, I determined that with my big head, I can only wear the Zulu’s for 3 hours max and then my head needs a break.  I don’t know if this is due to my hat size or the headsets and since I can’t use another head other than my own for a test control, I’m going to have to come to the verdict that they clamp just a little too tight for me (they might be fine for you).

Bose X

Since 1989 Bose has literally had a patent on ANC or active noise canceling headsets.  I can actually remember the first time someone told me about the Bose X.  How they are the best headset out there but cost almost $1000.  I remember thinking, a $1000? That’s crazy.  There is no way a pair of headsets could possibly be worth $1000.  Then I tried a pair on.  Wow.  I had to have one.  It took me a little while, but I did finally get a pair and I’ve never looked back.

Bose X from Amazon.com

Why I like them so much:

When you are a professional pilot it is not uncommon to spend 6+ hours a day in an airplane.  That is a LONG time to have a small vice-like-device strapped to your head. Even the slightest amount of pressure can grow to be a pain worse than death after 6 hours.   If you are wearing an uncomfortable pair of headsets for that long, you can go home with an absolute pounding headache.   That’s simply why, I like the Bose X.  Yeah they are quiet, yeah they are expensive but flat out they are the most comfortable aviation headset, period. They are ultra light and they are quiet.

My Verdict

Ok, so here is my summary.  If I have to sit in a piston engine airplane for less than 3 hours, the Lightspeed Zulus, I think, are quieter than the Bose and are my personal preferred choice.  In any jet aircraft, I prefer the Bose X because they are more comfortable for longer stretches of flying or for long duty days.  I actually prefer to use the Bose X in jet aircraft with the ANC feature turned off so that I can hear the aircraft and engine noises.  Even the passive reduction alone in Bose X is enough to block out the sounds you don’t want to hear (like environmental blowers and avionic fans).

So:

Piston Aircraft - Short Flights:  Lightspeed Zulu

Lightspeed Zulu

Purchase the Lightspeed Zulu’s from MyPilotStore.com

Jet Aircraft - Long Flights:  Bose X

Bose X Aviation Headset

Purchase the Bose X Headset from Amazon.com

Why do they gear aircraft engines to slow down the prop? In a C-421, why not let the prop spin at 2400rpm in cruise instead of gearing it to about 1800?

Hi Marty,

You’ve asked a good question and one that I asked myself when I first started flying Cessna 404s (which have the same engine and geared prop as the C-421)

I looked up my notes from Flight Safety and here is what I wrote (exactly):

“geared - quieter - turn at lower RPM and a little more power”

Hmmm, not much help.  A little more digging into my Cessna 404 Flight Safety Manual and I learn:

“All Cessnas, except the 421 and 404 series, have nongeared propellers mounted directly to the engine crankshaft. The 404 and 421 series include a reduction gear driven by the crankshaft to provide a 2.3 ratio between engine and propeller rpm.”

And my last source (and this is the best) is from “Aircraft Systems for Pilots” by Dale de Remer and it reads:

“The increased brake horsepower delivered by a high-horsepower engine may be the result of increased crankshaft RPM. It is therefore necessary to provide reduction gears to limit the propeller rotation speed to a value at which efficient operation of the propeller is obtained. Whenever the speed of the blade tips approaches the speed of sound, the efficiency of the propeller decreases rapidly.”

So Marty it sounds like that the McCauley 3 blade constant speed props that are found on the Cessna 404 and 421 have a ideal RPM range and the 375 horsepower engines (Teledyne Contiential tubro-charged GTSIO-520-M) might provide a little too much power at full RPM to the prop.  To fix this they insert a reduction gear between the crankshaft and prop so that the prop turns a little slower and falls within the propeller’s efficient operating speed.

I hope this helps and thanks for your question.

Fly Safe.

How do I calculate a headwind or tailwind?

This calculation is very easy using a mechanical flight computer such as an E-6B . The E-6B is a circular slide rule that has two sides: the computer side and the wind side.  The computer side which contains several scales and windows is used to solve ratio problems such as time-speed-distance, fuel and several other conversions.  The wind side is used to find both a aircraft ground speed and WCA (wind correction angle).

To help guide you through the wind side of the E-6B, I’ve created a short video tutorial showing how to calclate a tail wind or headwind for a particular flight plan.

A good friend suggested that I take some time to read the “Civil Pilot Training Manual”, which I am doing now.  This manual, developed by the Civil Aeronautics Administration in 1941 is the template that every pilot training manual and textbook in existence today is based upon! And that is no exaggeration.   In this book, on page 102 I stumbled upon “Figure 73 - Plan for Demonstration Model”.  One of the reasons I like this model is because it has markings for flaps, elevator and rudder. It would be a great aircraft to teach about the three axis of flight (longitudinal, lateral and vertical) and the basic aircraft structures.

I scanned the template in, enlarged it slightly (the one in the book is much too small) and saved it as a PDF that is available now in the download section of askacfi.com.

My recommendation would be to make the demonstration model a little robust by making the airplane out of some heavy cardstock. You can do that by:

1) Printing the template out on normal paper. Make your own carbon paper by taking a lead pencil and heavily shading the outline on the reverse side of the paper

2) By tracing and heavily pressing on the outline you can easily transfer the template to your own chosen cardstock paper.

3) Cut where indicated and fold where directed.

Download the template here:

Aircraft Demonstration Model Template

p.s. it doesn’t fly very well (at least for me).

Pilot Mike writes:

Thought I’d throw this one over your way to see what your thoughts are. Hangar flying this question has yielded several different answers from both IR pilots and CFIIs… You are departing an airport on an IFR flight plan; the route is “direct” to your destination. Upon climb out, ATC gives you radar vectors around arriving traffic at another airport. After about 15 minutes away from your filed route, ATC asks, “What is your on course heading?” Which heading do you provide back to ATC? Some different answers I’ve been told: 1. The heading direct to your destination from your present position 2. Heweeading to intercept your original filed route. 3. The original on course heading as filed. What is the appropriate response to ATC?

The appropriate response to give ATC is your heading that you would need to fly from your present location to the fix as specified in ATC’s request.  Why would controller need this information?  Well, I forwarded this question to Paul from FAAfolies.com and here was his response:

There are a variety of reasons the controller might need to know the heading; you’d think it doesn’t matter since the a/c has direct nav capability but it might be to see what the winds are, or there might be traffic to parallel, or other reasons.

I also called my local approach control facility and their answer was that many times the destination or next fix is defined to ATC in terms of lat/long coordinates.  You can only imagine how difficult it would be for a controller to know the on-course heading difference to a place that is 39N 34 55 versus 40N 05 10.

So what I do when ATC asks me? Well, to be honest, I just normally look at my GPS or FMS PFD and find the BRG or DTK field:

Colin ProLine DTK Field

The course in that field, is the number I usually respond to ATC with.  Any technically it isn’t a “heading” and it doesn’t help ATC know what the winds aloft are but I haven’t gotten any complaints yet.  Again, the feeling I got from ATC was that they are just looking for a general idea of which way your going to turn to proceed to that fix.  If they need left or right of that course for traffic sepeartion, they are going to tell you to turn.

Thanks for your question Mike and….

Fly Safe.

Unfortunately, because of my training and my flight schedule, I’ve fallen a little bit behind with some flight training questions here but I just received a question from Andrew that I’d like to answer.  Andrew asks:

I have a rotorcraft private and i would like to get my Single engine private. How many hours do i need in single engine to get my rating?

Hi Andrew,

You want to look at 14 CFR 61.109 - Aeronautical experience private pilot.

As a rotorcraft private pilot I’m guessing you already meet the 40 hour requirements, so now all you have to do is

Flight Training

meet the specific time requirements for airplane single engine.  These requirements are:

• 3 hours of cross-country flight training in a single-engine airplane;

• 3 hours of night flight training in a single-engine airplane that includes 1) One cross-country flight of over 100 nautical miles total distance; and 2)10 takeoffs and 10 landings to a full stop (with each landing involving a flight in the traffic pattern) at an airport.

• 3 hours of flight training in a single-engine airplane on the control and maneuvering of an airplane solely by reference to instruments

• 3 hours of flight training in preparation for the practical test in a single-engine airplane, which must have been performed within 60 days preceding the date of the test

• 10 hours of solo flight time in a single-engine airplane, consisting of at least 5 hours of solo cross-country time; One solo cross-country flight of at least 150 nautical miles total distance

So it kinds of depends on how you divide up the lessons with your flight instructor, but you know that you’ll need at least 10 hours of solo and probably another 20-25 hours of dual given from an instructor.  You’ll use this time with the instructor to prepare you for your solo, cross country training and then of course the checkride test preparation.  I’d budget at least 35 hours of flight training for your private pilot single-engine add-on.

Again, reference 61.109 for more information and here is the link to that CFR:

http://tinyurl.com/rb2b5k

You also might want to reference the private pilot PTS:

http://www.faa.gov/training_testing/testing/airmen/test_standards/pilot/media/FAA-S-8081-14A.pdf

Look on page 26 of this pdf.  On that page, you’ll see an “Additional Rating Task Table.”  That task table is useful for knowing what specific tasks you’ll have to complete on your checkride given your current ratings and certificates.

Thanks for stopping by the site and let me know I can be of any further help.
Fly Safe.

So what the heck is a Q-route?

Well.  There are primarily three types of airways:

1) VOR Federal airways - This is the airway system that most pilots are most familar with.  This includes your typical low alitudes “V” airways and the high-altitude “J” routes.

2)  Colored Federal Airways - There are still 49 of these airways still in existence.  LF and MF and they can be found mostly in Alaska.  They are designated by their color names Amber, Blue, Green or Red and then either a one or two digit number, i.e. “A 7″

3) RNAV airways - This is the latest and greatest route system found in our nation’s airspace.  The foundation of the RNAV route system started in 2000 with industry operators requesting the FAA to increase the use of RNAV to help navigate the nation’s airspace.  The advantages of the RNAV system?  Reduced mileage, reduction of conflicts between routes, and additional routes within the same airspace.

There are two types of RNAV routes:

1) Q-routes (high) are available for use by RNAV equipped aircraft between 18,000 feet MSL and FL 450 inclusive. Q-routes are depicted on Enroute High Altitude Charts.

A typical Q-route

1) T-routes (low) are available for use by RNAV equipped aircraft from 1,200 feet above the surface (or in some instances higher) up to but not including 18,000 feet MSL. T-routes are depicted on Enroute Low Altitude Charts.

A typical t-route

So now a good follow-up question would be, “Can you file and use a Q-route below FL180?”  and you see, we the staff at askacfi.com have thought ahead and already answered that one for you and you can read the answer to that question here.