To me, the most beautiful sound in the world is the spool-up of a turbofan engine. It gives me chills every time. Years ago at my home base airport, our flight academy building was located across from our mother FBO. We shared ramp space with transient parking, and if I happened to be walking across the ramp when a jet began its start sequence, I'd always stop and listen. There's just no other sound like it. I'd wait for the "click, click, click..." and then hear the whine start to sing as the turbine began spinning faster and faster. Major cool. I'd always grin, and I still do.
A jet takeoff would bring business to a standstill for a few seconds inside the flight academy building as everyone inside peered out the window and listened to the engines roar. Nothing inspires me more than watching and listening as a jet rockets down the runway and leaps into the sky.
For the turbine-challenged (or unexposed), which many piston pilots are, here are the basics of turbofan operation. Surprisingly, jet engine operation is much more simple than piston engine operation. A turbofan engine consists of three major parts: the compressor section, the ignition/combustion section, and the turbine section. Air is sucked into the engine by a series of compressor fans at the front of the engine. The speed of the first and largest compressor fan is expressed as a value of N1 in the cockpit. After intake air is compressed it enters the ignition/combustion section. Here the compressed air is mixed with fuel and ignited. The expanding gas then accelerates over the turbine causing it to spin very quickly (turbine speed is expressed as a value of N2 in the cockpit). The burned fuel/air exhaust gas then travels out the back of the engine through the exhaust nozzle. The spinning turbine, in turn, spins the compressor fans and the process becomes self-sustained. Bleed air from an auxiliary power unit is often used to set the engine into this self-perpetuating motion on startup.
The hot exhaust gas stream out the back of the engine results in high pressure behind the engine. Because the pressure in front of the engine is much lower than behind it, the engine (and airplane it is attached to) are sucked forward. This works similarly to how an airfoil produces lift. Airplanes fly by altering pressure around them, and they are quite literally being sucked upward and onward. Many older jets express engine power in terms of engine pressure ratio (EPR). EPR (pronounced "e-per," if you want jet pilots to think you're cool) compares the pressure at the back of the engine to the pressure at the front of the engine. The larger the difference, the greater the power.
Modern turbofan engines are high bypass engines, meaning most of the intake air bypasses the engine core and is simply accelerated and directed out the back of the engine. High bypass engines are quieter and more efficient. If you've ever seen an old military fighter takeoff and noticed black exhaust streaks behind it, it was probably a low bypass turbojet engine. Those black streaks are basically unburned fuel.
A byproduct of jet engines is bleed air. Bleed air is compressed air that is "bled" from the engine during some stage of the compression process. It is directed away from the engine and is used for ice control and environmental control purposes. Because the bleed air is hot, it can be circulated through engine nacelles and leading edges of the wings to heat them up for anti-ice functionality. The remaining compressed air is usually directed into the cabin for pressurization and heating or cooling. In some jets, engine bleeds must be left off during takeoff so all available intake air can be used for the production of thrust. Flight crews refer to this as a "bleeds off takeoff," and it's normally performed on shorter runways and/or at high density altitudes and high weights. Just like a good hunter doesn't waste any animal, a jet engine doesn't waste any of its capability to produce power and useful bleed air.
Another cool thing about turbofan engines is that their thrust production is non-linear. On takeoff, for example, as the airplane accelerates down the runway, more and more air is being rammed into the engine because of the increase in speed. This is called "ram recovery." Because the engine is moving through the air faster, more air is being gulped in for compression and the engine produces more thrust. This means the rate at which the airplane accelerates down the runway increases during the takeoff run. It is, indeed, a spirited affair.
Jet engines, they're a thing of beauty. Extremely reliable, efficient, and incredibly sexy. And they sing so beautifully, like a serenade to my ears.
(Citation CJ1 engine start) http://www.youtube.com/watch?v=L8TboIEJyg8
Wednesday, January 27, 2010
Thursday, January 21, 2010
Shallow and Coordinated
The FAA is concerned about low altitude stall/spin accidents these days. As well they should be. Quite a few of these accidents have happened in the past, so they've become a focus area. They're rather scary, too. Being low and [usually] slow, banking steeply, stalling and spinning in with no room for recovery is a grim scene. Luckily, there are things that can be done to protect you from becoming a stall/spin statistic.
Low altitude stall/spin accident usually happen in the traffic pattern, often during the turn from base to final. A tailwind on base is usually a contributing factor because it sets the stage for an overshoot of final, which invokes potential for a steepening bank at low altitude and airspeed. To make matters worse, the steep bank is often cross-controlled because the pilot subconsciously tries to cheat by turning the nose of the airplane back toward the runway using rudder. The steep bank plus the added adverse yaw most likely calls for opposite aileron deflection. The steep bank and increased load factor causes stall speed to increase exponentially and rapidly, the wing stalls in an uncoordinated turn, and presto, a spin is born. The base-to-final turn is usually executed below five hundred feet, so there's no room to recover and an almost certainly fatal crash results. It happens fast.
This does not have to happen to you. All that's required is a little vigilance in the pattern, and bank and airspeed discipline. Limit banks made in the traffic pattern to no more than thirty degrees. This will guarantee stall speed won't spike suddenly when you have little airspeed in the bank. Banking steeply causes a sudden withdrawal to your angle of attack margin savings account as the margin between current angle of attack and critical (stalling) angle of attack is cut exponentially. And during a phase of flight where airspeed isn't on your side you can't afford to make large withdrawals like that without changing something first. Banking can be thought of as a form of withdrawal from your angle of attack margin when airspeed remains constant, so limiting banking at low airspeed and altitude ensures you won't suffer an overdraw when you least desire it. Make a policy that banks in the pattern can never be steeper than thirty degrees. If greater bank is required because of an overshoot of final, the only option would be a go-around and an earlier turn to final on the next approach. There is never a reason to roll steeper than thirty degrees when a go-around is available.
In addition to the low altitude thirty degree bank limit, focus on making coordinated turns in the pattern. Your turns should always be coordinated, but this is even more important when low to the ground and slow. An airplane simply can not spin unless it is uncoordinated, so even if a stall occurs, if it's coordinated it will almost certainly be recoverable. Stall recoveries usually don't require more than one hundred feet, but spin recoveries can require thousands. Keep your turns coordinated and you'll never have to worry about spinning. Cross-check your inclinometer ("ball") and make sure it stays centered throughout the turn. When the airplane is coordinated, it's very unlikely for the wings to stall unevenly, so that protects you from entering a spin.
Of course, proper airspeed control is also important. Getting low and slow while banking is not a low risk form of flying. Keep the proper amount of airspeed in the bank to stay healthily away from a stall. But, remember, stalling is ALL about angle of attack. A gust of wind can change the wing's angle of attack, so in gusty conditions it's wise to carry extra airspeed (proportional to the velocity of the gusts). Bank angle increases load factor, and increased load factor causes stall speed to depart from the numbers in the POH and the arcs on the airspeed indicator and rise quickly. That's why banking should only be done conservatively in low altitude/low airspeed situations (i.e. the traffic pattern).
Don't forget to anticipate tailwinds on base, too. A tailwind on base calls for an earlier-than-normal turn to final. Anticipating this will reduce your likelihood of feeling tempted to over-bank to re-align with the runway. If you do overshoot, though, that's one of the worst places to bank steeply and a go-around should be given serious consideration.
Keeping your turns shallow and coordinated in the traffic pattern will offer your reliable protection from low altitude stall/spin accidents. It's a simple way of setting safety boundaries during low altitude/low airspeed operations.
Low altitude stall/spin accident usually happen in the traffic pattern, often during the turn from base to final. A tailwind on base is usually a contributing factor because it sets the stage for an overshoot of final, which invokes potential for a steepening bank at low altitude and airspeed. To make matters worse, the steep bank is often cross-controlled because the pilot subconsciously tries to cheat by turning the nose of the airplane back toward the runway using rudder. The steep bank plus the added adverse yaw most likely calls for opposite aileron deflection. The steep bank and increased load factor causes stall speed to increase exponentially and rapidly, the wing stalls in an uncoordinated turn, and presto, a spin is born. The base-to-final turn is usually executed below five hundred feet, so there's no room to recover and an almost certainly fatal crash results. It happens fast.
This does not have to happen to you. All that's required is a little vigilance in the pattern, and bank and airspeed discipline. Limit banks made in the traffic pattern to no more than thirty degrees. This will guarantee stall speed won't spike suddenly when you have little airspeed in the bank. Banking steeply causes a sudden withdrawal to your angle of attack margin savings account as the margin between current angle of attack and critical (stalling) angle of attack is cut exponentially. And during a phase of flight where airspeed isn't on your side you can't afford to make large withdrawals like that without changing something first. Banking can be thought of as a form of withdrawal from your angle of attack margin when airspeed remains constant, so limiting banking at low airspeed and altitude ensures you won't suffer an overdraw when you least desire it. Make a policy that banks in the pattern can never be steeper than thirty degrees. If greater bank is required because of an overshoot of final, the only option would be a go-around and an earlier turn to final on the next approach. There is never a reason to roll steeper than thirty degrees when a go-around is available.
In addition to the low altitude thirty degree bank limit, focus on making coordinated turns in the pattern. Your turns should always be coordinated, but this is even more important when low to the ground and slow. An airplane simply can not spin unless it is uncoordinated, so even if a stall occurs, if it's coordinated it will almost certainly be recoverable. Stall recoveries usually don't require more than one hundred feet, but spin recoveries can require thousands. Keep your turns coordinated and you'll never have to worry about spinning. Cross-check your inclinometer ("ball") and make sure it stays centered throughout the turn. When the airplane is coordinated, it's very unlikely for the wings to stall unevenly, so that protects you from entering a spin.
Of course, proper airspeed control is also important. Getting low and slow while banking is not a low risk form of flying. Keep the proper amount of airspeed in the bank to stay healthily away from a stall. But, remember, stalling is ALL about angle of attack. A gust of wind can change the wing's angle of attack, so in gusty conditions it's wise to carry extra airspeed (proportional to the velocity of the gusts). Bank angle increases load factor, and increased load factor causes stall speed to depart from the numbers in the POH and the arcs on the airspeed indicator and rise quickly. That's why banking should only be done conservatively in low altitude/low airspeed situations (i.e. the traffic pattern).
Don't forget to anticipate tailwinds on base, too. A tailwind on base calls for an earlier-than-normal turn to final. Anticipating this will reduce your likelihood of feeling tempted to over-bank to re-align with the runway. If you do overshoot, though, that's one of the worst places to bank steeply and a go-around should be given serious consideration.
Keeping your turns shallow and coordinated in the traffic pattern will offer your reliable protection from low altitude stall/spin accidents. It's a simple way of setting safety boundaries during low altitude/low airspeed operations.
Sunday, January 17, 2010
New York SFRA
In the aftermath of the August 8, 2009 mid-air collision killing nine over the Hudson River, the FAA has implemented a new Special Flight Rules Area (SFRA) for the New York City terminal airspace. Having just completed the recommended training on the new SFRA, I thought I'd offer a summary of the new rules.
Essentially, the new SFRA works to group aircraft into similar types of operations (transient or local). Mid-air conflicts arise when airspace becomes congested with aircraft of dissimilar performance characteristics, missions, and types of operations. The SFRA attempts to reduce traffic conflicts by creating a more orderly flow of traffic over the Hudson and East Rivers.
Hudson River Exclusion (Transient and Local Operations)
If you wish to conduct a transient operation (flying from one end of the Hudson River to the other without maneuvering or loitering), you've got two options. First, you can transition the class Bravo airspace above the Hudson river (with an ATC clearance, of course) if you wish to operate at or above 1,300' MSL. Second, you may operate in the "Hudson River Exclusion" between 1,000' and 1,299' MSL without an ATC clearance. Local operations operate over the Hudson River below 1,000'.
Transient operations are expected to "keep right" over the Hudson River. Meaning, southbound flights should fly along the west side of the river, and northbound flights should fly along the east side of the river.
East River Exclusion
The FAA does not distinguish between transient and local operations for aircraft flying over the East River. The East River Exclusion extends from the surface to the floor of overlying Class Bravo airspace and does require an ATC clearance to operate within.
Hudson and East River Exclusions
There are some general rules that pertain to both Exclusions:
Essentially, the new SFRA works to group aircraft into similar types of operations (transient or local). Mid-air conflicts arise when airspace becomes congested with aircraft of dissimilar performance characteristics, missions, and types of operations. The SFRA attempts to reduce traffic conflicts by creating a more orderly flow of traffic over the Hudson and East Rivers.
Hudson River Exclusion (Transient and Local Operations)
If you wish to conduct a transient operation (flying from one end of the Hudson River to the other without maneuvering or loitering), you've got two options. First, you can transition the class Bravo airspace above the Hudson river (with an ATC clearance, of course) if you wish to operate at or above 1,300' MSL. Second, you may operate in the "Hudson River Exclusion" between 1,000' and 1,299' MSL without an ATC clearance. Local operations operate over the Hudson River below 1,000'.
Transient operations are expected to "keep right" over the Hudson River. Meaning, southbound flights should fly along the west side of the river, and northbound flights should fly along the east side of the river.
East River Exclusion
The FAA does not distinguish between transient and local operations for aircraft flying over the East River. The East River Exclusion extends from the surface to the floor of overlying Class Bravo airspace and does require an ATC clearance to operate within.
Hudson and East River Exclusions
There are some general rules that pertain to both Exclusions:
- Do not exceed 140 knots indicated airspeed.
- The use of navigation/position lights is required (if equipped), even during daylight hours (as is the use of anticollision lights, but those would be required anyway). The use of landing lights is also recommended.
- Self-announce your position on the appropriate radio frequency for the Hudson River or East River. Frequencies can be found on the New York TAC chart.
- You must have a current New York TAC chart onboard and be familiar with the information contained therein.
The New York Terminal Area Chart contains the info you need to navigate the SFRA, including locations of mandatory position reports that are required to be made on the appropriate advisory frequency.
Local operations (below 1,000' MSL) that wish to circle the Statue of Liberty should circle counter-clockwise.
That sums up the major points of the New York SFRA. Although specific training is not required to operate within the SFRA, it is recommended. Visit FAASafety.gov to take the free training course.
Tuesday, January 12, 2010
Drawing Lines in the Sky
It is well documented that pilots who fly multiple instrument approach attempts to an airport are engaging in high risk flying. Many pilots crash on a second, third, or fourth (or more!) approach attempt in bad weather. This is why it's illegal for air carriers to attempt an instrument approach to an airport when the reported weather conditions are below minimums. Many pilots have perished while "taking a peek" on an approach. If the advertised weather at the field is below the approach minimums, don't peek, just divert. Peeking often involves fudging on minimums, and fudging often involves crashing.
If memory serves me, I remember reading about a pilot of a single engine airplane who crashed after seven approach attempts to an airport in bad weather. Seven! What was he thinking (or rather, not thinking)? So, what caused this pilot to crash? Was it the low weather? The approach procedure? The airplane? None of the above. It was the human that caused the crash. Clearly, this pilot deviated from the charted approach procedure and wandered into a dangerous area. Had the pilot not strayed from the charted procedure's courses and/or altitudes, he would not have crashed. No one has ever come to grief while flying on the final approach course at or above the minimum descent altitude (MDA) or decision altitude (DA). It just doesn't happen.
During the descent out of the enroute structure and into the approach structure the risk level is continuously rising. If only we had a "current risk level" gauge on the panel, color coded in green, yellow, and red arcs. Instead, we must visualize this in our minds throughout the various phases of flight. As we descend closer to those things which can hurt us, terrain and obstructions, we must be extra careful. When I'm flying IFR, I like to think of the ground beneath me as a spike pit. Airports are small areas carved out of the spike pit that are safe for airplanes to touch. The approach phase requires us to operate closer to the spike pit for a longer period of time than any other phase of flight. Because we can't see the spikes (trees, antennas, structures) while operating in clouds, one of the simplest and most definite ways of staying safe is to follow the lines and altitudes drawn on the approach chart. The chart could be thought of as a treasure map showing the only tried and true way through the cave to the destination. Deviating from the published path will lead you into uncertain and dangerous conditions. That's what happens when pilots "duck below" the MDA or DA to try to get a better view. The spikes get them.
When I reflect on accidents involving multiple approach attempts like the one above, I become aware of the true problem which causes these accidents. Lack of discipline. Every approach procedure should be flown exactly the same. They would be if pilots would let them be. If pilots would simply follow the charted procedure exactly, we would see no IFR approach accidents. Every instrument approach procedure is guaranteed to keep the airplane safely away from terrain and obstructions if it's flown and adhered to properly. It's when pilots stray from the beaten path out into uncharted airspace that they find trouble lurking in the gray. The pilot who flew seven approaches, however foolish, still wouldn't have had to crash on the last attempt had he just followed the charted procedure.
The approach phase of an IFR flight requires the greatest level of discipline and strict adherence to course and altitude guidance. The only way to avoid flying into something we can't see is to draw lines in the sky, and never cross those lines for any reason. Approach charts draw those lines for us. They're clear and simple, and we're prohibited from crossing them because danger lurks on the other side. Instrument approach procedures promise to keep us safe as long as we promise to never stray from them. If you reach the missed approach point and don't absolutely positively see the runway, you've reached the line drawn in the sky on the approach and you must immediately and enthusiastically initiate a missed approach. That's the only way to stay safe for sure. Venturing across that line is a massive gamble; you may or may not crash, but you're guaranteed to at least come closer.
Sometimes humans overthink things. That can lead to trouble on an instrument approach. The best way to fly an approach is to keep it very simple. Runway environment not in sight at the decision altitude? Simple: Go missed. Don't wait, don't hope, just move on to the next course of action. Multiple approach attempts are situations where pilots are likely to cross lines drawn in the sky, and unless there was some major weather event that might indicate the weather has improved for the next approach, don't do this. If the approach was flown properly the first time and it resulted in a miss, the same will be true the second and third time. Diverting to an alternate is a good way of ensuring you won't cross the line into unprotected and dangerous airspace.
If memory serves me, I remember reading about a pilot of a single engine airplane who crashed after seven approach attempts to an airport in bad weather. Seven! What was he thinking (or rather, not thinking)? So, what caused this pilot to crash? Was it the low weather? The approach procedure? The airplane? None of the above. It was the human that caused the crash. Clearly, this pilot deviated from the charted approach procedure and wandered into a dangerous area. Had the pilot not strayed from the charted procedure's courses and/or altitudes, he would not have crashed. No one has ever come to grief while flying on the final approach course at or above the minimum descent altitude (MDA) or decision altitude (DA). It just doesn't happen.
During the descent out of the enroute structure and into the approach structure the risk level is continuously rising. If only we had a "current risk level" gauge on the panel, color coded in green, yellow, and red arcs. Instead, we must visualize this in our minds throughout the various phases of flight. As we descend closer to those things which can hurt us, terrain and obstructions, we must be extra careful. When I'm flying IFR, I like to think of the ground beneath me as a spike pit. Airports are small areas carved out of the spike pit that are safe for airplanes to touch. The approach phase requires us to operate closer to the spike pit for a longer period of time than any other phase of flight. Because we can't see the spikes (trees, antennas, structures) while operating in clouds, one of the simplest and most definite ways of staying safe is to follow the lines and altitudes drawn on the approach chart. The chart could be thought of as a treasure map showing the only tried and true way through the cave to the destination. Deviating from the published path will lead you into uncertain and dangerous conditions. That's what happens when pilots "duck below" the MDA or DA to try to get a better view. The spikes get them.
When I reflect on accidents involving multiple approach attempts like the one above, I become aware of the true problem which causes these accidents. Lack of discipline. Every approach procedure should be flown exactly the same. They would be if pilots would let them be. If pilots would simply follow the charted procedure exactly, we would see no IFR approach accidents. Every instrument approach procedure is guaranteed to keep the airplane safely away from terrain and obstructions if it's flown and adhered to properly. It's when pilots stray from the beaten path out into uncharted airspace that they find trouble lurking in the gray. The pilot who flew seven approaches, however foolish, still wouldn't have had to crash on the last attempt had he just followed the charted procedure.
The approach phase of an IFR flight requires the greatest level of discipline and strict adherence to course and altitude guidance. The only way to avoid flying into something we can't see is to draw lines in the sky, and never cross those lines for any reason. Approach charts draw those lines for us. They're clear and simple, and we're prohibited from crossing them because danger lurks on the other side. Instrument approach procedures promise to keep us safe as long as we promise to never stray from them. If you reach the missed approach point and don't absolutely positively see the runway, you've reached the line drawn in the sky on the approach and you must immediately and enthusiastically initiate a missed approach. That's the only way to stay safe for sure. Venturing across that line is a massive gamble; you may or may not crash, but you're guaranteed to at least come closer.
Sometimes humans overthink things. That can lead to trouble on an instrument approach. The best way to fly an approach is to keep it very simple. Runway environment not in sight at the decision altitude? Simple: Go missed. Don't wait, don't hope, just move on to the next course of action. Multiple approach attempts are situations where pilots are likely to cross lines drawn in the sky, and unless there was some major weather event that might indicate the weather has improved for the next approach, don't do this. If the approach was flown properly the first time and it resulted in a miss, the same will be true the second and third time. Diverting to an alternate is a good way of ensuring you won't cross the line into unprotected and dangerous airspace.
Sunday, January 3, 2010
"Intercept the Localizer..."
"Cherokee five mike charlie, turn left heading 120, intercept the runway 8 Left localizer." Most instrument pilots have received an ATC instruction like this, but many don't understand its meaning. Implicit in this instruction is a limit not to descend or otherwise fly the approach procedure via your own navigation. Some pilots confuse this instruction with an approach clearance and believe they're cleared to descend and fly the charted procedure. Not yet. That clearance will most likely come shortly.
When a controller issues an instruction to "intercept the localizer," he's giving you a simple lateral instruction, much like an instruction to join an airway. He does not expect you to do anything other than just what he said, join the localizer. You might also hear a controller use this phraseology in lieu of "intercept." "Join the localizer" carries with it the same meaning and expectations. Turn onto the localizer, fly it, and await further clearance. DO NOT fly the approach procedure until you hear the words "cleared for XXX approach." You're not authorized to descend or make any turns called for by the approach until you've received approach clearance.
When a controller does issue an approach clearance, he's releasing you from his instructions to fly the approach under your own navigation following the charted procedure's courses and altitudes. Until you hear those magic words, "cleared for XXX approach," the controller is keeping you tight on his leash and you must obey only his commands.
So, why do controllers issue instructions only to intercept the localizer instead of fly the approach? Controllers have rules about when they can issue approach clearances to aircraft depending on traffic and your distance and altitude from the airport or some other fix. The controller can't let you off his leash to conduct the approach procedure until certain conditions are met. He'll clear you when he can, and in the meantime maintain your assigned altitude and simply do as he says, intercept the localizer and track it inbound.
When a controller issues an instruction to "intercept the localizer," he's giving you a simple lateral instruction, much like an instruction to join an airway. He does not expect you to do anything other than just what he said, join the localizer. You might also hear a controller use this phraseology in lieu of "intercept." "Join the localizer" carries with it the same meaning and expectations. Turn onto the localizer, fly it, and await further clearance. DO NOT fly the approach procedure until you hear the words "cleared for XXX approach." You're not authorized to descend or make any turns called for by the approach until you've received approach clearance.
When a controller does issue an approach clearance, he's releasing you from his instructions to fly the approach under your own navigation following the charted procedure's courses and altitudes. Until you hear those magic words, "cleared for XXX approach," the controller is keeping you tight on his leash and you must obey only his commands.
So, why do controllers issue instructions only to intercept the localizer instead of fly the approach? Controllers have rules about when they can issue approach clearances to aircraft depending on traffic and your distance and altitude from the airport or some other fix. The controller can't let you off his leash to conduct the approach procedure until certain conditions are met. He'll clear you when he can, and in the meantime maintain your assigned altitude and simply do as he says, intercept the localizer and track it inbound.
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