Mar 8, 2007

A Day in the Life (14) Rolling on the ramp now...

A description of a typical day's flight from Montreal to Vancouver and back - as a backdrop for a detailed, non-technical description of what an airline pilot does. (check left hand column for series index).

Log Entry 2003 - A320 Capt - CYUL - Main Ramp

Elapsed Time: plus nine minutes… and counting…

I gently push the thrust levers forward — it’s a very small amount compared to other aircraft I’ve flown. This morning with our fully-loaded A320 I set the donuts to 32% N1*. There’s a slight pause as the engines rev up and the N1 needles rise to match the donuts and then ever so gently the aircraft begins to roll. The journey begins.

The Airbus thrust levers are not actually connected to anything in the classical sense. That is, there are no stainless steel cables running over pulleys and through raceways and bulkheads and around corners all connected together with nuts and bolts and cotter pins that need careful lubricating and tensioning to finally produce the required movement in the fuel control unit over a dozen meters away. Instead our A320 levers are electronic sensors which each transmit dual digital signals over individual electrical wires to each engine receiver where these signals are decoded then translated into precise adjustment to the fuel control unit. This makes some people nervous. Knowing the relative reliability of digital technology vs. mechanical systems, and the amount of research that went into “fly-by-wire” before it appeared on airliners, I’m perfectly happy with it.

The morning’s hassles, chaos and procedural constraints fade away and I revel in the sensation of controlling the aircraft. With nothing more than my will expressed through feet and finger tips, I nudge along this finely-constructed marvel of science, art and technology. It’s a sweet sensation

The Airbus A320 is an excellent aircraft in all its derivatives. Whether I’m flying the sporty 319, the family sedan 320, or the cadillac 321 I love the fact that it’s a finger-tip aircraft. No brute force required — in fact it’s a hindrance. This machine responds to gentleness and finesse and demands a deeper understanding of its auto-technical nuances than many other predecessors. Some pilots never become fully comfortable with the Airbus. Others come to know it well and enjoy it. But that’s like most airplanes. For every model of aircraft there’s some pilots that love ‘em, and some that don’t.

We gradually gain speed and I pull the levers back to idle. The less thrust I use in these confined ramp areas, the safer it is for the crews and equipment outside. Once the aircraft has gained some momentum I carefully apply pressure to first one then the other brake pedal.

These brake pedals are not actually connected to anything in the classical sense. That is there are not stainless steel cables… oh wait, I’m repeating myself (see the thrust lever explanation above). There is a short hesitation between pedal movement and the initial reaction at the wheel, so I’ve learned to push just a tad, then wait a second. Shuttle valves in the braking system must switch over from the parking system to the normal system. If they’re not working, it’s better to discover it at two knots, and not twenty.

Each pedal produces a perceptible drag on the airframe. “Brakes check,” I call aloud. FO Paula scans the appropriate gauge readings and responds, “pressures zero.”

That’s a strange call to anyone who doesn’t know the Airbus. Similar checks on other aircraft would result in calls like "three thousand," confirming the hydraulic pressure available to drive the brakes. But on the Airbus we’re ensuring the normal system has taken over from the parking system by observing that the residual brake pressure has fallen to zero. Our actual hydraulic pressure is being monitored by ECAM and he’ll let us know if he doesn’t like it.

I add just a touch more power to slowly accelerate to full taxi speed.

Elapsed Time: plus ten minutes… and counting…

Random engine footnotes:

* A320s are powered by either the CFM-56 engine which uses N1 to set power or the V2500 which uses EPR (Engine Pressure Ratio). This link discusses the relative merits of the two methods.

*Donuts: A small circle on the rim of the main power indicator shows the power being commanded by the thrust lever angle (TLA). I can usually guestimate pretty closely how much power it will take based upon the particular airplane and the weight.

For some strange reason I’ve found that the smaller, lighter A319 needs just a little more N1 to get rolling than its big brother A320. I have no real idea why, but I suspect it may just be some difference in the indicator system. The maximum we’re supposed to use is 40%. I’ve only had to use that much during an outbound ground delay at Lagurdia on a hot summer day while taxiing with just one engine running. Parts of LGA are soft asphalt probably built on re-claimed swamp/shoreline. The tires seem to settle into a self-made low spot after just a few minutes.

Jet blast hazards:
United Airlines training video:

NASA discussion paper:


DeAnn said...

Excellent glance at the fly by wire stuff ... If I understand correctly, there's a delay in the relay ... ~D

Aluwings said...

Built on old 286 microprossors ?...i.e s-l-o-w b-u-t r-e-l-i-a-b-l-e ... ?