Friday, November 14, 2014

Kick It Out?

The following video has been making the rounds on the interwebs, showing a landing on runway 27L at Chicago O'Hare on a windy day last week:

I initially thought the plane was an AA 737, but closer inspection shows it to be a JungleBus operated for AA by Republic Airways. I have about 5000 hours in the airplane and have made my share of crosswind landings up to and including the published demonstrated crosswind limit of 38 knots (one of which was on 27L at ORD, actually). At NewCo this was considered a hard limit inclusive of gusts, and our FAA principal inspector later lowered our limit to 28 knots steady with gusts to 38. The airplane handled crosswinds very well, with more than enough rudder authority even at 38 knots crosswind component, and enough nacelle and wingtip clearance to use proper wing-low crosswind technique. In big wind, you'd start to kick out the crab and establish the aileron input just before beginning the flare, at about 50 feet.

The technique shown in the video has been criticized by some pilots, and it's definitely not ideal (especially considering the crosswind component was only 15-20 knots), but I don't think the landing was nearly as hairy as the video shows. This was shot from a long ways off using a very high-zoom lens, which greatly exaggerates angular differences (note that 27L looks about 4000' long and 400' wide!). I would guess they landed with somewhere around 5-10 degrees of crab - again, not ideal, but likely within design limits for JungleBus' robust landing gear. Looking at the video, it appears that the pilot attempted to kick out the crab late in the landing flare and didn't put in a corresponding aileron input, which rolled the plane a bit left, where the wind caught the upwind wing, so they touched down on the downwind gear while still crabbed.

I think most airlines would prefer the occasional sideloaded landing to a wingtip or nacelle strike, and for this reason many actually teach a wings-level crosswind technique. The idea is to wait until late in the flare and then kick out as much crab as possible just before touchdown; if you time it right, the plane will be aligned with centerline but on the ground before any side drift develops. You still use some upwind aileron, but only enough to hold wings level. This is a commonly taught technique on the 747 and 737 due to low nacelle clearance, on Airbus products due to the flight control software making cross-controlling difficult, and on the CRJ-200 and JungleBus' little brother JungleJet due to low wingtip clearance. I do not know whether Republic teaches the "kick it out" method on the JungleBus or the JungleJets operated by sister company Chautauqua.

In the JungleBus you have 16 degrees of bank before striking a wingtip or a nacelle. The former requires an unusually high pitch and the latter a nose-low attitude. When landing in 38 knots of crosswind, the most bank I ever saw was about 6-7 degrees. You're typically using Flaps 5 with a lot of wind additive, so you're looking at approach speeds of 140-160 knots depending on weight. There's no reason to use the "kick it out" method; the plane sideslips and lands beautifully on the upwind main wheel with perhaps 3/4 rudder deflection and 1/3 aileron deflection on touchdown, and increasing the aileron deflection throughout the landing roll greatly aids in keeping the plane tracking down centerline. It's not very different to how I land the Cub.

The Mad Dog absolutely hates being landed with any crab at all; doing so nearly always results in a nasty bounce and dramatic gyrations as the tires skip across the runway. For this reason my airline teaches a very similar wing-low technique to the one I used in JungleBus, with cross-control inputs made somewhat lower but still fairly early in the landing flare. There is less wingtip clearance on the Mad Dog than JungleBus, and the ailerons are far less effective (they're manually controlled via cables to servo tabs); the control wheel is close to full deflection on touchdown at the crosswind limit of 30 knots. I know this because a few days before the above video, I landed in Atlanta with winds 310 at 38 knots (twice in one day, actually).

It's easy to pile on the pilots in the video above, but I can say that over the course of thousands of landings I've made some real doozies and was just fortunate that no cameras were rolling. The same goes for any professional pilot flying. The pilot may have well been planning on using a wing-low technique but got a last minute sinker and he was just trying to save it from a hard touchdown. The last few seconds before landing get really busy when the winds are howling, and not just because of the crosswind - it's because your airspeed is often bouncing around +/- 10 knots, and you're making fairly dramatic pitch & power changes in response to floaters and sinkers. At the end of the day, this guy landed on centerline, in the touchdown zone, at what looked like a fairly low sink rate, and the plane appeared to handle the sideload fairly well. This was one of the first windy days since last spring, everyone's knocking the rust off, and no doubt we'll all refine our technique considerably as winter approaches.