All this gets deep quickly, and it’s real easy to find oneself throwing out sound bites which, while mostly accurate, add up to a pitifully poor caricature of reality. Discovery, NOVA, and all the rest are notorious for this.
Speaking just to engines as an example …
- All jet engines take several seconds to go from idle to useful thrust. The Airbus is not unique in that regard. It’s simply a mattter of the physics of how they’re designed. Some are slower than others, some are quicker. Any given model is quite consistent though.
- Starting about 20 years ago jet engines began to have computerized fuel controls. Much as cars went from mechanical carburetors to modern computerized fuel injection. Jet engines are now available with several different versions of the fuel control program but otherwise identical hardware. An airline can decide to buy the lower-power engines or the higher-power engines. Same hardware, just a different rev limiter inside the software. The software can also be tuned for faster or slower engine acceleration. faster acceleration dumps more fuel in faster resulting in higher internal temps, which in turn directly cause greater wear, short life, etc.
Lower power and/or slower acceleration saves fuel in operation and costs less per hour in lifecycle maintenance. So often airlines opt for that. Other carriers, who may operate from shorter or higher-altitude airports or often operate the aircraft near max range = max weight may choose the higher/faster engine option because net net the extra performance pays for itself.
But whatever the program is, that’s what it is. It’s factually accurate but logically invalid to say something like “the engine accelerated slowly to save money/fuel.” The pilots at that carrier will be trained on, and come to know, the characteristics of their engines. From their POV, characteristics are what they are.
2.a Having said that, it’s not uncommon for engines to have different idle modes. Flight, ground, approach, and landing could each have a different idle setting & therefore different acceleration time curves. Approach is the critical one and would tend to be hghest idle = quickest acceleration. These various modes are automatically selected by the aircraft logic and are subliminal to the pilot.
3. Pilots critically need to have an accurate visceral “feel” for how long engine acceleration takes to safely operate near the corners of the envelope. As well as a solid & accurate awareness of altitude & altitude trend and most of all speed & speed trend.
It *is *fairly easy to get into a crack where you figure out too late that you’re in a crack. And then instantly moving the throttles to full power is too late to save you. This is a risk every day on every flight during the approach & landing. The answer is to know the trap is there and stay far enough away from the edge that you don’t get suckered.
In day-to-day airline ops it’s easy to stay far enough from the trap that we don’t fall in. Although I’d wager that every day someplace around the world some airliner has a closer-than-desired call with falling out of the approach & landing short due to pressing too close to the edge.
The airshow flyby we’re all taking about was emphatically *not *day-to-day airline ops. The show profile they planned was truly maximum performance. Which is another way of saying zero margin for error. Through some combination of poor planning, poor execution, or poor understanding of the nooks & crannys of operating the airplane on the edge (which really falls under poor planning), they drove into a crack the couldn’t drive out of.
If the pilot was expecting approach idle but the airplane was actually running in landing idle mode (for legit or malfunction reasons) , that could be the straw which broke the camel & “caused” the mishap.
All the above only scratches the surface of just engine acceleration issues. There’s another half-dozen engineering factors which NOVA, Discovery et al talked about which could also be de/re-constructed to provide teh rest of teh nuance points to a lay audience. And probably a half-dozen human factors as well. This stuff is not simple. These are among the most highly engineered things mankind knows how to build.
4. I’m not trying to hang the pilot. This show maneuver should have been fully vetted by management & engineering & flown in the sim umpteen times. My bet, knowing a little of Airbus culture, is that both the engineers & the pilots hubristically assumed everything would work 100% as expected. Management gave a wink & nod & said “Let 'er rip!”, and the engineers & piltos gave it a quick once over in the sim.
At the moment of truth, I can’t say whether the pilot just goofed, or the instruments told a factually accurate but holistically misleading picture, or there was a software glitch / unexpected “feature” which threw a joker on the pile at the last moment.
But at the end of the day a very skilled aviator, much more skilled than I, ran a perfectly good airplane into trees by trying to do something the machine couldn’t do. Not wouldn’t. Couldn’t.
5. A very legit quetion about aircraft design philosophy is whether it’s a good thing to have airplanes with lots of “intelligence” in the very basics of power & attitude control. Smarts sound nice. But if they actually produce unpredictable or unexpected behavior in real time in extremis, we’d be better off with less smarts.
When it’s down to the nut cuttin’ & fractions of seconds matter, pilots are not going to deeply grok that Control Mode 12.a.4.c has activated and now this, that, and the *other thing *all now work dfferently. That’s now *couldn’t *shades into *wouldn’t *as seen from the cockpit.
My overall gut feel is Airbus has this problem but can’t / won’t admit their engineers have gone too far. But that’s gut. And as I said in another recent post in another thread, I’ve never flown Airbuses (yet), so my opinion should be taken as an interested & skilled observer, not an experienced participant.
