News today reported that a commercial airliner performed an emergency descent after losing cabin pressure. The oxygen generators that provide passengers with emergency O[sub]2[/sub] reportedly last for 15-20 minutes after ignition, so I guess they’ve got that big a window in which to descend to a safe altitude, but how rapidly can they make the descent?
Moreover, how do the configure for the descent:
-shallow descent path at high airspeed, with moderate drag (spoilers partially deployed), or
-very steep descent at low airspeed, with high drag (full spoilers, flaps, gear-down)?
In the former, a moderate-drag config would hold airspeed steady at a high-value, but in a shallow dive; the latter is a steeper dive, but the high-drag config should hold airspeed to a lower value. So which strategy provides the greatest vertical speed, and what other considerations come into play in deciding on how to get from cruise altitude to an altitude where supplemental O[sub]2[/sub] isn’t needed?
Not a pilot, but I was on a plane once from Providence, RI to Houston. Midway through the flight, they made an announcement asking if a physician was on board. One was, and he determined that a passenger was suffering from a heart attack, and needed to get to a hospital immediately.
The pilot came on and told us that we were diverting to Nashville, TN. He then appeared to point the plane to the ground. It was the fastest descent I’ve ever experienced. From the time the pilot made the announcement (presumably at cruising altitude) to the time we landed was about 10 minutes.
As we sped down the runway after landing, we could see ambulance lights racing toward the plane. These two guys rushed on who looked like they were ready for anything. They had latex gloves and masks on, had all kinds of medical gear strapped on, not to mention holstered pistols. They had the guy off the plane in less than a minute and into the ambulance.
No one is certain, but it’s thought that a China Airlines 747 might have gone supersonic during an emergency descent in 1985. According to the Wikipedia article, “Altitude decreased 10,000 ft (3,000 m) within only twenty seconds.” and “They had descended 30,000 ft (9,100 m) in under two and a half minutes”.
That’s a bit faster of a descent than **Xema **cites, but it was also not exactly ‘controlled’. It does give you a bit of respect for the designers at Boeing, though…
No, they appeared to be firearms. They also had police badges. I guess they were a combination of paramedic and police, which is something that I’ve never seen before.
I remember that they had pistols in holsters on one hip, and big pairs of medical scissors on the other hip. They also had handcuffs.
“The examination of the DFDR readout disclosed a number of periods where data were lost. These data losses were the result of the vibration and the sustained vertical acceleration forces (Gs) exerted on the recorder during the descent. Some of these data were retrieved through the use of recovery techniques, but the accuracy of these recovered data is suspect. In addition, anomalies in the recorded altitude and airspeed values appeared early in the descent because the descent rate of the airplane had exceeded the maximum tracking capability of the airplane’s digital air data computer (DADC). Specific details are discussed below.”
“Between 1015:23 and 1017:15, the airplane descended from 30,132 feet to 9,577 feet. During this period, except for some short 3- to 7-second intervals of accurate data, the data recorded by the DFDR were, as stated earlier, either unreliable or erroneous.”
“The maximum vertical acceleration forces recorded during the descent were 4.8Gs and 5.lGs as the airplane descended through 30,552 feet and 19,083 feet, respectively. The 5.1G peak value was recorded on a portion of the tape where data had been lost originally and subsequently recovered, but this value is consistent with the adjacent data which show an arresting of descent rate and a pull-up.”
There were two “serious” injuries among the 274 people on board. I’d say this is probably provides an “upper limit” to the answer of “how rapidly *can *they make the descent?” , for aircraft in service today.
on a 3-degree descent path (e.g. on final), my understanding is that full flaps and gear-down requires a significant application of power to maintain ~160-170 knots. I would think that idling the engines and adding in full spoiler would allow a considerably steeper descent path without exceeding the flaps-down speed limit. The question is whether the vertical speed in this case would be greater than the vertical speed for some other configuration with a higher forward speed, e.g. spoilers-only or spoilers w/gear-down. If Whack-a-Mole’s cite is accurate, then it appears spoilers w/gear-down is the fastest way to descend from cruise altitude to an altitude safe for an unpressurized cabin.
Took a plane into Burbank airport in CA. For noise abatement purposes they needed a steep descent, flaps out, gear down. The plane shook like a paint mixer as we headed down. Several passengers were horrified, and I wasn’t thrilled either. Sitting next to me was a pilot hopping a free ride, chugging beers from a cooler he carried on. He said not to worry about it, perfectly safe, but he’d downed at least 10 cold ones already. The plane pulled up to a shallow descent rapidly and landed smoothly. I prefer other airports.
I checked with another airline pilot friend - who now flies for Citation Shares.
He said the 747 is a bit too clean and heavy for outstanding performance in this competition. Heavy, the best it can safely do is not much more than 6000 fpm; lightly loaded, 8000+.
The champion is apparently the DC-8, whose thrust reversers can be activated in flight (not true for any Boeing he’s flown). He didn’t know the exact figure, but guessed it could easily be 12000+.
A second QANTAS jet in less than 24 hours has had an inflight incident. The 747 returned to its origin only 30 minutes into the flight because of engine problems. They did not want to descend too quickly, either.
