I was saddened to learn today of a Cirrus SR20 that crashed into a Manhattan skyscraper, killing Cory Lidle, the New York Yankees pitcher, and Tyler Stanger, a 26-year-old flight instructor from California. As it happens, I was at the exact same spot yesterday, en route to the Downtown/Wall Street heliport in a Robinson R44. I have flown my own Cirrus SR20 all the way to the Arctic Ocean and then southwest to Alaska. Friends have thus been asking me to speculate on how this accident might have occurred.
The airspace around New York City is extremely complex (chart). There are three Class B airports, LGA, JFK, and EWR, and therefore a lot of protection for jets flying in and out of these busy airports. You can’t be anywhere near the city unless you are talking to New York Approach, the tower controllers for one of those airports, or over the Hudson River between the surface and 1100′ above sea level (i.e., pretty darn low).
I have often been confused about the East River. Careful study of the helicopter and terminal area charts has led me to conclude, mistakenly, that it is not legal to fly too far north of the Brooklyn Bridge without explicit clearance from LaGuardia Tower on 126.05. As Lidle and his instructor probably knew from talking to local experts, it is in fact legal to continue up to Roosevelt Island, at 86th St., without talking to LGA. In any case, if you continue straight ahead up the river indefinitely without getting clearance (which is easy to get), you are very seriously violating LGA’s airspace. If discovered, the FAA could have suspended the pilot or instructor certificates of anyone on board the aircraft.
My preliminary best guess (and at this point it can only be a guess) is that the two pilots on board the accident SR20 were cruising slowly up the East River. At some point, they decided that they’d reached the end of the little cut-out tongue of uncontrolled airspace over the East River. They attempted a 180-degree turn in an attempt to get southbound down the river toward uncontrolled airspace. An airplane in a sharp turn stalls at a much higher airspeed than when straight and level. Merely by putting the airplane into a steep bank and trying to hold altitude, they could have gone from flying to an aerodynamic stall (wings at too high an angle to the relative wind or, in simpler terms, air not moving fast enough over the wings) in a matter of seconds. At this point, the airplane is not easily controlled and a lot of bad things can happen. Low-speed low-level maneuvering, which typically happens when aircraft are trying to land, is the leading cause of plane crashes.
[It is possible to turn an airplane tightly and safely and is commonly done inside mountain valleys in Alaska (where guys just love to take off and head towards a pass to see if there is any separation between the clouds and the terrain; if not, they turn around and go back to their cabin). The trick is to slow down as much as possible. An ice skater going fast will use up a lot more ice in a 180-degree turn than an ice skater going very slowly. In an airplane, this means putting out flaps so that you can fly slower without stalling and slowing down to maybe 1.5 times stalling speed (in the Cirrus SR20 this would be about 75 knots with two people on board). At a slow speed, you have to be somewhat careful with bank angle because you are closer to the stalling speed. On the other hand, you don’t need a steep bank angle to make a tight turn because you’re only going about as fast as a car.]
[Thursday update: I was interviewed by a New York City radio station this morning. The interviewer, as have most journalists, seemed very interested in the Cirrus’s parachute. People can’t shake the idea that a plane with a parachute is safer than a plane without one, though in this situation, the safest plane would have been an old slow cheap one that could be flown slowly and therefore turned tightly. The Cirrus is a great plane for going straight and level on a 400-mile trip, but its virtues become liabilities when trying to fly low and slow.
http://cbs4boston.com/video/?id=25043@wbz.dayport.com is a video clip from the local TV news station that flew with me and Alex this afternoon]
[Saturday update: found a good table of airspeed/bank versus turn radius: http://selair.selkirk.bc.ca/aerodynamics1/Lift/Min_Radius.html ; my example above of slowing the Cirrus down to 75 knots would enable a turn diameter of 1000′ at a comfortable, yet steep-by-Private-pilot-standards, 45-degree bank angle. The East River is approximately 2000′ wide. At a more standard slow pace for a Cirrus of 100 knots and 30-degree bank angle, the turn diameter is 3075′.]
Full post, including comments 