Category: Flying

Due to a large number of fatal crashes during training, students are not allowed into a Robinson R22 2-seat helicopter, even with an instructor, until they’ve had some ground training.  If you believe that you have some special mission on this planet the grounnd training might cause you to terminate your.

Here’s what I learned about the hazards inherent in flying helicopters…

As with airplanes, the key to being safe in a helicopter is energy management.  In an airplane you have potential energy (altitude) and kinetic energy (forward speed) that can be traded off against each other to bring the airplane down gently in the event of an engine failure or ordinary landing.  The helicopter has three kinds of energy:  potential (altitude), kinetic (forward speed), and angular momentum (blade speed).

In an airplane you can make decisions about trading forms of energy very late in the day.  For example, if you pull the stick all the way back at 6000′ above the ground you will gradually slow down and eventually stall and perhaps enter a spin.  With many airplanes you could spin nearly all the way to the ground before applying forward stick and opposite rudder to get back to a normal flight condition.  All without an engine.

In a helicopter, by contrast, if the blades spin down more than 10-15% from their normal velocity, there is no way to convert potential or kinetic energy into spinning such that the helicopter will start to fly again.  If you don’t have an engine, therefore, your helicopter can very quickly become a rock.

In a turbine-powered helicopter like the Jet Rangers that are typically used for sightseeing the blades are heavy and the blades won’t slow down for several seconds after an engine failure.  The Robinson, however, is designed for super high efficiency and therefore everything is as light as possible.  After an engine failure you have no more than 1.2 seconds to take exactly the right actions or the helicopter cannot be recovered.

What if you do take all the right actions?  Suppose that you’re up at 4000′ and the engine quits.  You lower the collective pitch (lever on your left) immediately to flatten the blades and allow them to be driven by the wind through which the helicopter is now falling at 2000 feet-per-minute.  You adjust the cyclic (stick in front of you) for about 65 knots of forward speed.  You aim for a landing zone.  The good news is that you don’t need a very large one but the bad news is that the glide ratio is 2:1 instead of an airplane’s 10:1 and therefore you don’t have as large an area from which to choose.  As you get within about 50′ from the ground you pull back the cyclic to flare the helicopter and shed most of the forward speed.  Just as in an airplane this flare also arrests most of the vertical speed.  At the second to last moment you stop flaring and return the helicopter to being parallel to the ground.  Ideally at this point you are hovering 5′ or so above a soccer field and the blades are still spinning.  Finally you raise the collective as the helicopter falls, using the stored energy in the blades against the force of gravity.  You land gently on the skids.  (In practice the cyclic flare is more important than the “hovering autorotation” at the end; a lot of people walk away from helicopter engine failures if they get the cyclic flare right but can’t manage to pull the collective smoothly at the last moment.)

This all sounded good until we looked at the “deadman’s curve”.  The marketing literature for helicopters says “if the engine fails, you can autorotate down to a smooth landing.”  The owner’s manual, however, contains a little chart of flight conditions from which it is impossible to landing without at least bending the helicopter.  Unfortunately these conditions are the very ones in which nearly all helicopters seem to operate.  If you’re above 500′, for example, you’re pretty safe.  But TV station helicopters are often lower than that when filming.  Flying along at 65 knots is also good but if the camera needs the pilot to hover the helicopter slows to a crawl.

After a couple of hours of theory we went to the hangar and preflighted the helicopter.  The engine is flapping in the breeze on an R22 and therefore you can inspect a lot of linkages and lines that are hidden on most airplanes.  Most of the other critical mechanical components are open to the air or accessible via covers that you open during the inspection.

Four hours after the lesson started we were ready to fly…  but the ceiling was 900 overcast with visibility 4 miles in mist.  So we gave up and went home.

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A Vancouverite pointed out that one can fly from downtown Vancouver to downtown Seattle on http://www.helijet.com for $120 each way (full fare, unrestricted) and that this service has been around for many years.  Boston/NY is a bit farther but should be doable for $200 (the Delta Shuttle’s full fare is $226 one way).

A Sikorsky S-76 helicopter holds 12 passengers and costs $3000 per hour to charter, perhaps half that to operate all day every day.  The new S-92 holds 19 passengers and the brochure claims that you can run it for $2200 per hour.

It will take about 1.25 hours to get from Boston to New York.  Assuming that we get 15 passengers on the average trip in an S-92, there would be a fat profit if we could collect the same price as the Delta Shuttle folks.

Where to land?  The Museum of Science in Boston has a heliport and there are several options in Manhattan, including the Port Authority’s heliport.  Rudy Guiliani had been closing heliports because he claimed that the deafening noise and pollution of burning hundreds of gallons of jet fuel per hour somehow degraded quality of life.  Fortunately the new mayor, Michael Bloomberg, has his own personal helicopter and will presumably be more sympathetic to the transportation needs of the elite.

[A bit of searching at http://registry.faa.gov reveals that Michael Rubens Bloomberg has instrument, multi, and helicopter ratings.]

So folks, what will it be?  The $10 Chinatown-Chinatown bus, AMTRAK’s Four Hour Fast Train (TM), or our new hypothetical helicopter?

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Yesterday I flew from Bedford, Massachusetts to Gaithersburg, Maryland.  East Coast airspace was complex to begin with and has become further complicated by restrictions around the Washington, DC are.  If you’re an instrument-rated pilot you can avoid all of this complexity by filing an ins trument flight plan and taking advantage of Air Traffic Control (ATC) services.  The assigned route took me straight over JFK airport at 6000′ and then through central New Jersey before proceeding over Balitmore-Washington Intl. airport and into the Montgomery Country Airpark.

My Diamond Star (DA40) is a brand-new design but it uses an engine that hasn’t changed for 50 years.  Old-style piston airplane engines require that the pilot constantly adjust the air-fuel mixture as the plane rises into thinner air or descends into denser air.  When you’re done with your flight and parked at the airport, you pull the mixture control all the way back to “full lean” and the engine stops, starved of fuel.

Descending out of 6000′ over Baltimore I noticed that my exhaust gas temperatures were rising, despite the fact that I was enriching the mixture.  Between talking to ATC and the other pilots at the busy non-towered Gaithersburg airport, I didn’t have much time to reflect on this odd behavior.  After parking the airplane I pulled the mixture control back.  The engine kept running.  I shut the airplane down by shutting off the flow from the fuel tanks, then hopped out and unscrewed the cowling.

The mixture control itself is an L-shaped arm on the throttle body of the fuel injection system.  It is attached to the mixture cable by a bolt.  In case the mixture cable snaps, a spring is also attached to the arm to pull the mixture to “full rich” (engine runs but not necessarily efficiently).  Sadly the engineers at Diamond decided that both the spring and the cable should be attached with the same bolt.  The bolt was rattling around loose in the bottom of the cowl.  The spring was hanging free.  The end of the mixture cable was hanging free.  My engine continued to run because (a) I had been conservative in running moderately rich at altitude, (b) the difference between 6000′ and sea level isn’t enormous, and (c) the L-shaped arm, free to rattle around a bit, hadn’t rattled its way to “full lean”.  [This is more than a theoretical possibility; rumor has it that a plane similar to mine landed in a farmer’s field in the Midwest back in the Spring of 2002 after the mixture cable came loose.  The incident led to a redesign, which was retrofitted to my airplane in June 2002.]

My mixture control was held together with a regular bolt and a locking nut (that apparently did not lock and is now on the ground somewhere between Long Island and Baltimore).  Tull, one of the best mechanics at Gaithersburg, happened to be on the field at 6:00 pm on a Saturday and he reassembled the airplane, this time using a bolt with a little hole in the middle so that a safety cotter pin could be inserted to prevent future separations.

There are a bunch of ways to look at this incident.  One is despair at the state of engineering in this world.  Had an extra hole been drilled in the L-shaped arm, the spring could have been attached separately from the mixture cable.  The engine would have gone to full rich after the mixture cable detached.  Alternatively, Diamond could have used a bolt with a hole in the middle and a safety, like the one that the mechanic in Gaithersburg used.  A few extra cents and the plane would have been spared the risk of an emergency landing.

Another way to look at this incident is to be ever-vigilant when flying a piston single-engine airplane: have an emergency landing spot in mind at all times. The #1 reason for engine stoppage is running out of gas but it apparently is not the only reason.

Project for today:  make it to Williamsburg, Virginia with both the airplane and myself in one piece.

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One of the hazards of wealth and/or hanging around with rich people is the possibility of dying in a small airplane crash.  If you’re an average schmoe you’ll wear a rut in the pavement between house and job, be entertained watching TV on the sofa, watch your kids get on the schoolbus every day, and drop dead of obesity [should say “average American”, I guess] at age 83.4.  The rich, however, must shuttle among their 5 luxury homes and get their kids to and from exclusive private schools in the countryside.  Shuttling requires many private airplane flights, not least because the luxury homes may be on islands where airplanes provide the only access.  If you want to escape the rabble you have to go somewhere that is impractical to read by car and that isn’t so populated that it merits daily Boeing 747 flights.

A couple of recent airplane crashes, however, have got people scared.  One involved Minnesota Senator Paul Wellstone and an April 4 crash here in Massachusetts involved M. Anthony Fisher, a real estate tycoon from New York.  Both were in Beech King Air airplanes, each of which had two engines and two professional pilots.  Both were doing non-precision instrument approaches in bad weather.  In both cases people initially suspected icing, a terrifying flight hazard in cold-weather clouds but one that the King Airs are reasonably well-equipped to handle.  In both cases the actual cause appears to have been that the airplane was simply flown too slowly and fell out of the sky, which is by far the most common way to crash an airplane for all levels of pilot.  People fear engine failure but they die from pulling the stick back too far.

Let’s start by looking at the most recent crash, which involved Bob Monaco, a pilot based from our local airport (Hanscom Field in Bedford, Massachusetts, BED).  Today’s Boston Globe carries a story that is typical for (a) being filled with errors, and (b) not providing the URL where readers could find the original National Transportation Safety Board report and study it themselves.

The goal of the trip was to fly the rich family up to a prep school that the daughter was considering attending, then take the rest of the family and its interior designers out to their house on Martha’s Vineyard.  The pilot, Bob Monaco, planned the flight initially from New York to Bedford, a large civil/military airport with a 7000-foot main runway and an instrument landing system (ILS). 

Background on aerodynamics:  Airplanes hold themselves up by pushing air down.  In flight, an airplane’s wings are angled up. As the plane moves forward this angled surface pushes air downward and, as a reaction, the airplane rises up (Newton’s 3rd Law). Air weighs a lot less than the metals and plastics in the airplane and therefore one must push a lot of air down in order to pull the plane up, which is why wings are so physically large.  An airplane must maintain a reasonably high forward speed for the wing to do its job; a wing that isn’t moving pushes no air down.  If a pilot, in attempting to slow down for landing, slows down too much the plane will “stall” and become hard to control.  If the pilot does not immediately push the stick forward to pitch the airplane down and pick up more speed, the plane may go into a “spin” and start to fall out of the sky.  A plane can be recovered from a spin but usually this requires more altitude than is available if the spin happens while approaching to land.  Turning an airplane uses up lift that would otherwise be available to hold altitude and therefore an airspeed that works for level flight will result in a stall in a tight turn.

Background on flying in the clouds:  An ILS approach is referred to as a “precision approach”.  Under normal circumstances the Air Traffic Controllers (ATC) give you radar vectors and altitudes to fly until you intercept the radio beams of the ILS.  They are required by regulation to set you up so that you need not make more than a 30-degree turn to get onto the ILS, i.e., ATC points your airplane more or less straight in toward the landing runway.  Once established on the ILS you make very small adjustments in pitch and bank to keep the needles centered and set the engine power so that your airplane holds a slow steady speed (pointing the nose down toward the ground would normally build up a lot of speed so you cut engine power from its cruise setting to reduce the total amount of energy being put into the system).  Notice that at no time on an ILS is the airplane required to make a turn; the airplane is going slow but flying straight.

At Bedford the ILS 29 approach lets you go down to 300′ above the ground without seeing anything, then, if you can see the runway lights you’re allowed to go down until you’re just 100′ above the ground.  In an emergency you wouldn’t worry about ever seeing the runway but keep flying the needles until the wheels slammed down on the pavement (they do this in training in Europe, actually).

Not only does an ILS provide low minimums but it also generally comes with assistance from ATC.  If you’ve somehow gotten very confused or your equipment isn’t working right and you’re off-course or at the wrong altitude, they’ll probably call you on the radio (they are invariably polite and ask you to “say altitude” or “say position”, hoping that you’ll discover your mistake, rather than “you’re in the wrong place, bozo”).

A non-precision approach is a much more complex procedure that (a) requires a bunch of turns in the clouds, fairly slow and low to the ground, (b) makes the pilot(s) solely responsible for the airplane’s position, and (c) requires the airplane to stay at a higher altitude if the pilot cannot see the runway.

Why would you ever do a non-precision approach?  For the airlines the answer is generally that you don’t.  You fly from ILS-equipped airport to ILS-equipped airport.  If there is no ILS at an airport that you wish to serve, you twist the government’s arm into installing one.

On April 4, Bob Monaco changed his plan, while in flight, to go from an ILS-equipped airport (BED) to a much smaller airport, Fitchburg (FIT) at which only non-precision approaches are available.  Because he is dead we can’t ask him why but we can presume that he got a weather report for FIT that said the clouds weren’t that low and FIT was closer to the prep school, thus saving 45 minutes of driving.

From the NTSB report, it sounds as though the clouds were right around 1000′ above ground level, which is the minimum height that Monaco was required to maintain above the runway until he could see it.  It sounds from the witness reports that he did not really see the runway until he was right on top of it.  At this point he was too high to land.  However, it is legal, assuming that you can maintain continuous visual contact with the runway, to make tight circles around the airport and then land, perhaps on a different runway than the one you were initially approaching.  You want the circles tight so that you don’t risk flying into more clouds.  Note that tight circles imply turns and that if you are hoping to land an airplane you want to be going slowly.  Recall from the aerodynamics paragraph above that turning makes it more likely that the airplane will stall at a given speed.

Even with two pilots on board, the challenge of keeping the runway in sight, setting the plane up for landing, and making those tight turns was apparently too great and the King Air crashed.  The NTSB report says that the airspeed indicators showed 60 and 66 knots on impact, which is a good speed for a little training airplane but much too slow for a King Air in a turn (the King Air’s typical approach speed is 100 knots).

If you’re planning to take a trip in a small airplane, what lessons can you learn from these mournful events?  First, legal does not equal safe.  One reason that the airlines have such a good safety record is that they are much more conservative than required.  For example, many airlines have found that their pilots are unable to maintain acceptable tolerances during circling-to-land approaches such as the one Bob Monaco was attempting and therefore they no longer train pilots on this procedure nor use it in operations.  Second, an ILS greatly enhances safety.  If the weather is marginal and your friend says “we’re going to the little airport at Gaithersburg, Maryland” repond with “I don’t mind driving an extra 20 minutes from Dulles or Baltimore-Washington International”.  Third, if you really want to be safe wait for the weather to improve.  Even with the best equipment and pilots, sunshine adds a big safety margin.

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