Pakistan plane crash: Jet carrying 107 people crashes into houses near airport

[Gabriel]

Firstly, the issue of operating time isn't about turnaround, it's about costs associated with operation including maintenance intervals and depreciable wear and tear.

Meh, most of that in pressurized transport category planes is defined by cycle and hours. When you use the plane mostly for short flights like PIA does the flight cycles limit is reached first so the hours don't matter much.

And I'm seeing around 8-12 minutes of operating time shaved off here.

How so? I see 3 minutes at most. Don't confuse how short was the descent/approach with how much time they saved, because they made the descent shorter by making it steeper which means that they flew MORE time at cruise.

then a steep idle (OP DES) drop

It is the 2nd or 3rd time that you mention this. Do you have anything against and idle descent in open descent mode (i.e. speed-on-pitch)? For me it is the correct way to descend if not using VNAV.

Dumb, yes. Crazy, indeed. Dangerous, or course. Diabolical, quite. But what if he'd pulled this off dozens of times? And what if management had rewarded him for his fuel conservation and flight time? It might start to look pretty smart.

HE was management. Hence why the Smartwings incident reminded me of this PIA one.

I am with you that he likely attempted some improvised fuel/time saving profile. But I don't think that the profile they ended up flying was what he had in mind. For example, I don't think that he intended to cross the threshold at 210 knots. I think they screwed it up even by their standards, and then were stubborn and arrogant to fix it in a proper way and instead attempted to salvage it. And they would have gotten away with it if it wasn't for the mysterious reason that they retracted the landing gear.

[Evan]

No, I wouldn't.

I don't think that the airline was counting with the 3-minutes reduction in the turnaround time as to squeeze another flight in the day, nor that repeated 3-minutes savings throughout the day would be enough to squeeze in another flight. At the same time, I don't think that the crew would make any less money for saving 3 minutes of flight, otherwise it would be an incentive to make the flight last more, not less. So with all that, the differential cost of operating time is about zero.

Additionally, the flight profile they flew doesn't seem to be the one you would if you wanted to minimize time, which is extend cruise as much as possible then idle and full flight speedbrakes fully extended to Vmo down to 10000 ft, level off still with speedbrakes and idle, slow down to 250kts, continue descent with 250 kts, speedbrakes and idle until about 2500ft ARL and 10 miles out, then level off and extend landing gear and slats flaps as soon as speed allows (you are still at idle and with the speedbrakes extended for as long as the combination of speedbrakes and flaps setting is legal) and intercept the glide slope while doing so, arriving at final approach speed when you are at about 1500 ft, then retract spoilers (if still extended) and add approach thrust to stabilize the approach and do the before landing checklist finalizing just before the 1000 ft gate.

This is not only the fastest descent/approach but also a very fuel-saving one, although not as much as gliding from as far as possible which was the previous one I mentioned.

Again, I see everything you are saying but I don't think you see what I am getting at.

Firstly, the issue of operating time isn't about turnaround, it's about costs associated with operation including maintenance intervals and depreciable wear and tear. And I'm seeing around 8-12 minutes of operating time shaved off here. Multiply that by hundreds of flights a year. From a dirt cheap operator perspective.

But, as far as technique is concerned, I'm speculating that a pressured directive from on high might have led a pilot with an imperfect understanding of everything you stated above to recklessly improvise a technique. What he tried to pull off here is essentially what I described above: prolonged flight at cruise, then a steep idle (OP DES) drop to join the glideslope from above about halfway down it (at about 5nm, not 10nm) with flaps first coming out less than 6nm out and landing flaps coming out at 3nm. So more distance covered at cruise, the remainder flown on energy alone and half the normal distance of the final flown with drag out. Screw the placard speeds (please, he's done this a million times and nothing's fallen off) and there's always enough runway needed to stop despite the higher landing speed.

Dumb, yes. Crazy, indeed. Dangerous, or course. Diabolical, quite. But what if he'd pulled this off dozens of times? And what if management had rewarded him for his fuel conservation and flight time? It might start to look pretty smart.

The real danger lurked in what was missing. Stability. Checklist procedures. CRM. So on day zero speed got away from him, workload got compressed, things got skipped, confused or overlooked (like overspeed warnings and gear warnings), he failed to configure the gear and there was no redundancy to contend with these errors, zero margin for error.

That's becoming my theory for what it's worth.

[Gabriel]

Indeed, but we are dealing with crazy here. It would seem to me, if I place no value on safety (or the heightened possibility of a missed approach), that the most cost-efficient alternative (remember, the target is the best CI, a compromise between fuel conservation and operating time) would be to cover more distance in less time at cruise where the engines are most efficient and then to do the entire descent including most of the final 3nm at idle while having minimum drag out for as long as possible. Would you agree?

No, I wouldn't.

I don't think that the airline was counting with the 3-minutes reduction in the turnaround time as to squeeze another flight in the day, nor that repeated 3-minutes savings throughout the day would be enough to squeeze in another flight. At the same time, I don't think that the crew would make any less money for saving 3 minutes of flight, otherwise it would be an incentive to make the flight last more, not less. So with all that, the differential cost of operating time is about zero.

Additionally, the flight profile they flew doesn't seem to be the one you would if you wanted to minimize time, which is extend cruise as much as possible then idle and full flight speedbrakes fully extended to Vmo down to 10000 ft, level off still with speedbrakes and idle, slow down to 250kts, continue descent with 250 kts, speedbrakes and idle until about 2500ft ARL and 10 miles out, then level off and extend landing gear and slats flaps as soon as speed allows (you are still at idle and with the speedbrakes extended for as long as the combination of speedbrakes and flaps setting is legal) and intercept the glide slope while doing so, arriving at final approach speed when you are at about 1500 ft, then retract spoilers (if still extended) and add approach thrust to stabilize the approach and do the before landing checklist finalizing just before the 1000 ft gate.

This is not only the fastest descent/approach but also a very fuel-saving one, although not as much as gliding from as far as possible which was the previous one I mentioned.

[Gabriel]

ATL said this was a slightly-challengly-steep approach.

Where? Post # please?

Why do you insist with just the gear issue? They crossed the threshold at 210kts overspeeding the flaps. CLEARLY and UNDOUBTEDLY (yes black and white) the gear was not the ony issue here. Even if they had lowered the gear and gotten away with it, this would have been very very VERY bad airmanship worth of immediately firing both pilots and revoking their licenses for life (again, yes, black and white) (although that would have never happened because no one outside of the airline would have know it and the airline was encouraging this behavior).

[3WE]

Indeed, but we are dealing with crazy here. It would seem to me, if I place no value on safety (or the heightened possibility of a missed approach), that the most cost-efficient alternative (remember, the target is the best CI, a compromise between fuel conservation and operating time) would be to cover more distance in less time at cruise where the engines are most efficient and then to do the entire descent including most of the final 3nm at idle while having minimum drag out for as long as possible. Would you agree?

Put whatever you want in the rule book...

It won't replace fundamental knowledge, nor will it change the fact that ATL said this was a slightly-challengly-steep approach.

Are there any checklist items to check that the landing gear are down?

[3WE]

On most of my airliner flights in good weather, full flaps are selected way past the outer marker...Thus making for a much shorter stabilized approach and a potential reduction in safety.

Seems to me we need to ban all airplanes and publicly beat most pilots.

[Evan]

The most fuel-efficient feasible approach is one where you go from cruise altitude and cruise speed smoothly to 2500ft ARL and ~200 KIAS some 10 miles short of the runway, all the time at idle and with the airplane clean, you then have ~ 2 minutes (still at idle) to slow down to final approach speed as you progressively extend slats/flaps and gear and then, with the plane fully configured for landing, for the first time since you started the descent, increase thrust from idle to keep the approach speed and thus finally stabilize the approach, and complete the landing checklist as you arrive to the 1000 ft gate some 3 NM from the runway threshold.

There are crazier more efficient alternatives, but they are too crazy and the fuel gain is negligible compared to the one above.

Indeed, but we are dealing with crazy here. It would seem to me, if I place no value on safety (or the heightened possibility of a missed approach), that the most cost-efficient alternative (remember, the target is the best CI, a compromise between fuel conservation and operating time) would be to cover more distance in less time at cruise where the engines are most efficient and then to do the entire descent including most of the final 3nm at idle while having minimum drag out for as long as possible. Would you agree?

[Gabriel]

The most fuel-efficient feasible approach is one where you go from cruise altitude and cruise speed smoothly to 2500ft ARL and ~200 KIAS some 10 miles short of the runway, all the time at idle and with the airplane clean, you then have ~ 2 minutes (still at idle) to slow down to final approach speed as you progressively extend slats/flaps and gear and then, with the plane fully configured for landing, for the first time since you started the descent, increase thrust from idle to keep the approach speed and thus finally stabilize the approach, and complete the landing checklist as you arrive to the 1000 ft gate some 3 NM from the runway threshold.

There are crazier more efficient alternatives, but they are too crazy and the fuel gain is negligible compared to the one above.

[Schwartz]

There WAS a big focus on optimizing landings to conserve fuel, but right now that is out the window. But it will come back. I suspect you might be surprised at what type of approach is the most efficient. It probably means small changes in thrust, not zero and then max thrust.

[3WE]

Question is: could that be part of a flawed fuel conservation strategy to minimize flight time at low altitude?

Fast descents do not save fuel.

I guess that does make it a flawed strategy.

[Evan]

Basically ATC starts all jets down at the same distance out. Big jets can do that at idle, smaller ones need a little power to control it.

Yes but this one appears to have started down about 10 minutes late, perhaps intentionally. Correct me if I'm wrong but wouldn't the descent normally be initiated around 09:05 on the chart shown below?

I went through a few altitude graphs on FlightRadar24 showing AIrBlue A320 flights descending into Karachi. The descent/landing times from around FL350 were between 25 and 30 mins. PK8303 did it in about 18 mins.

Question is: could that be part of a flawed fuel conservation strategy to minimize flight time at low altitude?

[kent olsen]

Interesting. I flew 3 transport aircraft, DC-9, DC-8 (60/70 series), B-747 for two different airlines and we always descended at idle. That gave you about 2500-3000 fpm descent. Then I flew the Hawker 1000 and Citation X and you had to use a little power or you'd come down at over 3000 fpm. Basically ATC starts all jets down at the same distance out. Big jets can do that at idle, smaller ones need a little power to control it.

[3WE]

None of my three airlines preached such a thing.

I am struggling with Evan's ever present black and white mentality and how a few key adjectives totally flip the scale.

Jet Fuel used to be expensive and fuel savings were "of interest."

No doubt that can do some things to save fuel in how you operate.

That being said, somehow you are able to not_be stupid about it (maybe you are a genius and indeed you are not_Pakistani?)

A well planned descent without the use of spoilers (and NO need for excess speed)...Indeed it's good to not_be UNNECCESARILY dragging all over creation at low altitudes with full flaps and wheels out...If it works with ATC, (and again, you are not_stupid about it) kudos for you for protecting us from additional global warming....

But alas, I need to stick to cow farts and non-synthetic nitrogen sources.

[Evan]

None of my three airlines preached such a thing.

If the approach is not being conducted in adverse conditions that would make it difficult to achieve stabilized approach criteria, the final flap selection may be delayed until just prior to 1,000 feet above field elevation (AFE) to conserve fuel and reduce noise and emissions or to accommodate speed requests by air traffic control. This approach is known as a low‑drag, delayed-flaps, or noise-abatement approach. Note: The thrust required to descend on the glide slope may be near idle.

Also, one of their seven tips:

5. Avoid flying extended periods at low altitudes.

Now misinterpret that in the mind of a cowboy airman trying to please a penny-pinching boss in the absence of a functional safety culture.

- Stay at higher altitudes as long as possible.
- Descend with open descent mode, i.e. thrust at flight idle. Moderate speed with elevators and speedbrakes.
- Compress the flap schedule as close to landing as possible.

Now look at the actual approach profile of PIA 8303. Flaps 1 comes out less than 6nm from the runway and well over placard speed. He intercepts the GS at about 5nm but then gets a bit high again. He goes directly to flaps 3 at about 1500ft, again, well over placard speed. At 1nm out he is actually on the GS but has failed to manage speeds, configure the aircraft or complete the checklists. So too fast, not properly configured and, whoops, no gear.

8303 went from FL350 to the runway in about 18 mins. That seems to me to mean they delayed TOD by about 12mins. Why?

Makes me think there is a practiced technique here that didn't go so well this time.

Of course no airline with a valid safety culture would ever preach such a thing. But an airline that preaches skimping on fuel above all else is essentially preaching such a thing.

[Evan]

None of my three airlines preached such a thing.

How many of them were based in Pakistan?