Friends have been asking me how it is possible that the Asiana 777 landed short of the runway at SFO.
It turns out that the instrument landing system (ILS) glide slope was out of service. So the pilots were likely conducting a “visual approach”, i.e., looking out the window to see if the airplane was properly positioned to land. There are synthetic glide slopes available from WAAS-enhanced GPS receivers and there is a RNAV 28L approach at SFO that provides LPV minimums for such units. These cost about $500 to install in an experimental (uncertified) airplane, but regulation adds $10,000 to that cost when the gear goes into a certified airplane such as a four-seat Cirrus SR20. Touching even one screw on an airliner, after it leaves the factory, costs closer to $1 million. So it seems unlikely that Asiana had retrofitted their B777 with the latest WAAS GPS gear.
How hard it is to fly a visual approach? That’s how all approaches are flown in light piston-powered airplanes during training. Things move both a little faster with jets and a little slower. The speeds are faster, e.g., 120-145 knots on final approach instead of 60-70. What is slower is the response of the aircraft to power adjustments. Some of this is due to simple inertia. The airliner weighs a lot more. Some of this is due to the fact that jet engines, once “spooled down”, can’t provide instant power.
Here’s a story from my second month of flying regional jets for Comair, a Delta Airlines subsidiary. I am leaving the original language but adding notes in brackets because this was written for my pilot friends.
Today was a beautiful clear and calm day for flying. I took the CRJ [Canadair Regional Jet, a 50-passenger 53,000 lb. airliner] from RDU up to LaGuardia. The ATIS [canned weather broadcast, updated hourly] said that we could expect the ILS 22 at LGA. Our clearance was to descend and maintain 4000′, head for the Verrazano Bridge, then fly up the Hudson River. We were high and close to the airport, restricted to a minimum speed of 180 knots, when New York Approach cleared us for the “visual 22″. These are the toughest maneuvers for newbies because one has much less time to get stabilized than with a full ILS procedure and it is almost impossible to use the autopilot, which won’t intercept the radio beams at extreme angles.
The airline encourages us to fly 5 knots faster than “Vref” [around 145 knots in a CRJ with all seats filled] during training, in order to have a margin for error in case of wind gusts or incompetence. When a runway is short, however, the extra energy is difficult to dissipate and tends to result in significant float. The runway at LGA is 7000′. A test pilot demonstrated the ability to get the airplane stopped in about 3000′, but it wouldn’t necessarily have been consistent and it certainly would not have been comfortable for passengers. The minimum runway length that people regularly use for the CRJ is 6000′.
My approach was slightly fast and slightly high. I was reluctant to adjust the thrust in the last 300′ or so because we had been fairly stable on glide slope and on airspeed. In previous approaches I had tended to overcontrol. I started the round-out at the 1000′ markers, and touched down about 2500′ down the runway, applying moderate brakes and thrust reversers and turning off at Charlie, having chewed up almost 5000′ of runway (out of 7000′). Passengers complimented me on the smoothness of the landing, saying “It is usually rough here at LaGuardia” (of course it is usually rough because pilots more skilled than I are trying to get the plane on the ground, have the spoilers deploy, and stop the plane before it runs into a swamp).
Captain Mark said “That landing sucked. I’ve got 13,000 hours in this airplane. I’m going to show you how it is done on the next leg.” He then asked “Are you flying the airplane or is the airplane flying you?” When I asked for specific tips Captain Mark replied that I was an instructor and ought to be able to figure out what I was doing wrong. He grudgingly confirmed that I had left too much thrust in for too long.
We approached Charlotte, North Carolina in near perfect conditions. The weather was smooth and, due to some clouds at 2500′, we were given vectors for the full ILS 23 approach. [The controllers vectored us so that we were lined up with the runway approximately 10 miles from touchdown.] Captain Mark let the autopilot do most of the work, concentrating on getting the thrust exactly right for a stabilized approach. At about 200′ above the ground, Captain Mark disconnected the autopilot and transitioned to hand-flying. Somehow he ended up a little fast and also flared a bit too high. The CRJ is a very efficient glider and spooled down jet engines don’t supply the kind of drag that props would. The CRJ entered a shockingly efficient glide in ground effect at 10-15′ above the runway. We weren’t descending. We weren’t slowing down. The 7500′ runway was slipping away beneath us.
It is unclear how one would fix a situation like this. [In a piston airplane the best and easiest fix is to add power, retract the flaps, and climb away from the runway in order to try again; this can’t be done in an airliner due to the long spool-up time of the engines.] In a piston airplane you’d add a touch of power and pull back for a slower and less efficient airspeed. The airplane would sink due to loss of efficiency and the power would slow the vertical speed. In the jet, once the thrust levers are back it takes 3 or more seconds to get any significant power from the engine. Nosing the airplane forward would result in hitting the nose gear, which isn’t any better on a jet than on a piston four-seater.
After we had sailed over approximately half the runway, the airplane finally started to settle towards the surface. We touched with about 3000′ remaining [i.e., 4500′ down the runway, 2000′ more float than I experienced at LGA]. Captain Mark slammed hard on the brakes, to the point where the passengers probably would have said “ouch!”, and applied full reverse thrust. Tower called and asked “Are you going to be able to make Foxtrot?” This was the second-to-last taxiway and only about 500′ from the end of the runway. In fact, we did make Foxtrot, but only barely. We used just about a full 7000′ of runway. [I.e., at LGA we would have been nose-to-nose with the boats.]
What did I learn from watching a very capable guy with 13,000 hours of CRJ experience? That landing a CRJ consistently requires more than 13,000 hours of experience…
————— end of story from 2008
Additional background: The CRJ is an adapted business jet and, lacking leading edge devices or “slats”, lands much faster than a standard airliner such as a Boeing 737. In addition to the challenge of speed the pilot must, in the last 40-50 vertical feet of the flight, pull the airplane from its 3-degrees nose-down attitude to a standard nose-up landing attitude of about +9 degrees. (This lead one FlightSafety instructor to refer to every landing in a CRJ as a “controlled crash”. The procedure is different enough than in a Boeing or Airbus that the plane comes with a special briefing card for jump-seating pilots of conventional airliners so that they don’t start screaming in the last 30 seconds of the flight.)
Follow-up: Folks to whom I emailed the story asked me how the rest of the trip with this pilot went. My reply: “Captain Mark found fault with everything that I did for the next three days. I hadn’t ironed my shirts properly. I left my bags next to the airstair door while doing a preflight inspection, thinking that it would give the captain and flight attendant more space and freedom to put away their bags. Captain Mark admonished me “You have to go up into the airplane, put your stuff away, and then go back outside to do the preflight.”
Punchline: About six months later, US Airways 1549 was flying the same route (LGA to CLT) and went down in the Hudson River. Asked my opinion about the heroes Captain Sully and Jeffrey Skiles I said “Hey, Captain Mark and I took 50 passengers from LGA to CLT. We got them to the gate at Charlotte, on time, warm and dry, and nobody called us heroes.”