Ask The Pilot

[mjt57]

I've tried a couple of different styles of bifocals. Normal ones don't work at all, but I recently had a set made up in which the top third has a distance correction, and the lower two thirds are my intermediate. Again the junction aligns along the coaming. They work well.

I have a pair of safety glasses at work which are "multifocals". When I had my cataract surgery done I discovered that I needed, like eveyrone else my age, reading glasses. It was a PITA having to fish out the reading glasses, take off the non-prescription safety ones, read what I had to read and so forth.

Whilst the surgery corrected my acute astigmatism, these new prescription safety glasses made distance viewing go from "standard def" to "hi def" if you get my meaning.

But they require me to look up and down through them to read or to see.

First time outside I was walking down a steep set of stairs, I nearly took a tumble as I misjudged my step. At 130m above ground level it scared the cough out of me.

I'm used to them now after 4 years. But I suppose for you it's probably not worth it at this stage of your career, huh?

 

[suze2000]

This is OT, but I agree that multifocals take some getting used to. And also my first pair went straight back as the reading area was too narrow - impossible to find the focal point. Optometrist told me to ensure in future that I always ask for something called B-wide lenses - the Rolls Royce of multis, according to him. And yeah, the first time I wore them I almost fell down a set of stairs as well.

 

[jb747]

The issue with multi focus from a pilots' point of view, is that we need to look around the coughpit to find many of the things we constantly use. Whilst that is often a simple task, when flying on instruments, moving your head is a great way to induce vertigo. We all learn to keep our heads quite still, and to just move eyes to what we want to see. The upshot is that I'm quite happy with my look overs or bifocals...

 

[fresherbill]

Would the A380 have been Kai Tak-capable, had it been around at the time?

 

[jb747]

Would the A380 have been Kai Tak-capable, had it been around at the time?

Parking may have been an issue, but the aircraft would have had no inherent issues flying the IGS approach.

 

[jb747]

Sorry, in amongst all of that discussion about glasses, I didn't see you question.

In this AH report of a multi-engine failure on an SQ flight in 2015, one of the reasons was found to be (my bold):

What, in layman's terms, is IPC rotor path abradable lining material and what does it do, please? (Sure, I've Googled it, but mostly just refers to the SQ incident) Ever heard of it coming 'off' previously and causing engine issues?

Whilst it isn't something you'd expect, the edges of the blades do touch the casing of the engines at times. Here's some info on the coating...and I'd have to admit, I've never heard of it before.

Thermally sprayed abradable coating technology for sealing ... - Oerlikon

What I can't understand from the AH report is why both engines should surge and then stall at exactly the same time, if the offending material is somehow within each engine.

The dual surge is extremely unexpected. Not something I can explain. A wall of water could certainly effect both engines, but here they're saying that it was caused by the loss of some of this coating. I would not have thought there would enough of it there to do anything of the sort. Ah, I see that they say that it actually burns in the hot section, and that upsets the flows momentarily.

Also that the crew, after multiple stalling and self-restart of both engines, decided to continue to destination rather than diverting.

It's not really a 'self restart'. The engines have basically recovered with minor EEC activity as soon as the material stops burning. Release of some more causes another momentary surge. A surge that will require a shutdown will be associated with rapidly rising, and uncontrolled EGT. In this instance, even though the ECAM was still showing 'surge', I expect the the EGT was pretty much in the normal range. #1 was an intentional shutdown, and really shows a weakness in the ECAM design. In a dumber aircraft (without potentially misleading electronic checklists) I expect it would have been left running.

Also a bit surprised that the aircraft carried on 4 hours later, apparently without an internal inspection of engine #2.

I'm not surprised that they continued to destination. It's called 'press-on-itis'

 

[Boca68]

Last week, I flew QF27 SYD to SCL. In SYD, I noticed out the window a medium sized truck parked very close to the fuselage, just in front of the inner right hand side engine. For the life of me, I can't remember now what was written on the truck. (getting old) But I seem to remember something suggesting engine start up. As you can tell, I really didn't take a whole lot of notice.

But upon arrival in SCL, the Captain informed us that there would be a minor delay , because they had to keep one engine running until we could be connected to ground power. I'm assuming this is related to the truck on the tarmac. What could the problem be? APU? Or other? If the APU, were we lucky to flown in the first place?

Any thoughts on what it might suggest as a potential problem.

Apologies for the vagueness of the question

 

[jb747]

Last week, I flew QF27 SYD to SCL. In SYD, I noticed out the window a medium sized truck parked very close to the fuselage, just in front of the inner right hand side engine. For the life of me, I can't remember now what was written on the truck. (getting old) But I seem to remember something suggesting engine start up. As you can tell, I really didn't take a whole lot of notice.

But upon arrival in SCL, the Captain informed us that there would be a minor delay , because they had to keep one engine running until we could be connected to ground power. I'm assuming this is related to the truck on the tarmac. What could the problem be? APU? Or other? If the APU, were we lucky to flown in the first place?

Any thoughts on what it might suggest as a potential problem.

You need two things to get an aircraft to start. Electricity and an air supply. Normally the APU will provide them, but either or both can be provided externally. Once the engines are running, on a 747 the APU is nothing but a dead weight until it arrives at the next destination. It cannot be started in flight.

When we arrive at a port, the APU is started as we approach the gate. The air load is transferred by turning on the APU bleed, just prior to engine shutdown. The generators take over the load as the engine driven ones drop off line.

As you had to wait for external electricity, you either had a totally unserviceable APU, or you had one which could provide air, but not electricity. An APU being either totally, or partially, unserviceable is not a big issue, though it adds a few minutes to both departure and arrival procedures.

No APU, or one that cannot provide air, is a real PITA in hot conditions, as if forces us to rely on external air conditioning, which is never as good as the aircraft packs.

 

[Boca68]

You need two things to get an aircraft to start. Electricity and an air supply. Normally the APU will provide them, but either or both can be provided externally. Once the engines are running, on a 747 the APU is nothing but a dead weight until it arrives at the next destination. It cannot be started in flight.

When we arrive at a port, the APU is started as we approach the gate. The air load is transferred by turning on the APU bleed, just prior to engine shutdown. The generators take over the load as the engine driven ones drop off line.

As you had to wait for external electricity, you either had a totally unserviceable APU, or you had one which could provide air, but not electricity. An APU being either totally, or partially, unserviceable is not a big issue, though it adds a few minutes to both departure and arrival procedures.

No APU, or one that cannot provide air, is a real PITA in hot conditions, as if forces us to rely on external air conditioning, which is never as good as the aircraft packs.

Thank you JB, I do remember that the truck was definitely a generator or compressor as it had an exhaust located on the top of load space. But I only noticed it because I'd never seen it before.

Otherwise the flight was perfectly fine.

 

[Quickstatus]

How do aircraft air conditioning packs cool air when on the ground.

I understand that they don’t use the common refrigerants that are used in the usual air conditioners found in refrigerators or cars. It’s easy to envisage cooling of input air when outside air is -50C. But how does it work in the deserts of DXB?

Also when the packs dehumidify the air where does the water go. I don’t recall seeing any parked aircraft dripping water into a puddle on the tarmac like you would see a car producing a puddle of water underneath when the aircon is on.

 

[jb747]

I'd have to admit that my first answer was likely to be along the lines of magic. The start point is always extremely hot air, so the ambient temperature only affects the need for the air, more than the production. Looking the schematics in flight, it's generally at around the 200º mark!

Anyway, there is a very complete answer here:
https://www.quora.com/How-does-the-...ow-is-fresh-oxygen-provided-to-the-passengers

 

[Quickstatus]

Of course.

Precool the hot bleed air in heat exchanger with ambient air as coolant
Then compress the air which heats it up again but it’s now compressed
Then cool it using ambient air again as coolant in a heat exchanger
Then the bleed air is now near ambient temp after 2 stage cooling but compressed

Now the bit that I didn’t think of:
expand the compressed air through an expanding turbine - so the temp goes below ambient air temp and the energy gained help turn the compressing turbines

The water is used to cool the air compressors and heat exchangers which evaporates it - so no puddle.

 

[747sp]

Thank you for answering my questions. One more if i may. My flight was delayed a few weeks ago due to the late arrival of another flight that our Captain was flying. My question is can the copilot do parts of the pre flight checks pre the Captain's arrival or is the cross checking just too big of a component to make that option practical? It was a A330 .

 

[jb747]

Thank you for answering my questions. One more if i may. My flight was delayed a few weeks ago due to the late arrival of another flight that our Captain was flying. My question is can the copilot do parts of the pre flight checks pre the Captain's arrival or is the cross checking just too big of a component to make that option practical? It was a A330 .

Even if the other guy has already done the preflights for both PF and PNF, it will still take about 35 minutes at a minimum to get ready, starting from the point where your backside hits the seat. You have to check everything, plus get your head around this flight (as opposed to the last one he was on). Going faster means you are either skipping or missing things....

You don't just jump in and go....

 

[Boca68]

Of course.

Precool the hot bleed air in heat exchanger with ambient air as coolant
Then compress the air which heats it up again but it’s now compressed
Then cool it using ambient air again as coolant in a heat exchanger
Then the bleed air is now near ambient temp after 2 stage cooling but compressed

Now the bit that I didn’t think of:
expand the compressed air through an expanding turbine - so the temp goes below ambient air temp and the energy gained help turn the compressing turbines

The water is used to cool the air compressors and heat exchangers which evaporates it - so no puddle.

Interesting! Always presumed otherwise. Learn something everyday.

Reading JB's link, its not what I thought. (but I now know Boyles' + Charles' + Avogardos' = Ideal Gas law. perhaps the explanation of a fart? )

P.S. just threw the 'fart' in for humour, pre-empting any discourse.

Thanks again @jb747 and @Quickstatus

 

[jb747]

Here's a rather interesting video...

 

[Quickstatus]

Fisheye lens video camera on a gimbal?
Very stable image!

Something similar for your office?. Where could you mount it?

 

[mjt57]

Love these cameras. They use them on MotoGP bikes, but it's only of one perspective, facing forwards (and usually at the rider's butt).

 

[jb747]

Fisheye lens video camera on a gimbal?
Very stable image!

Something similar for your office?. Where could you mount it?

The 380 has nowhere near the range, or rate, of movement to make it even slightly interesting. You may as well attach it to a rock.

 

[RooFlyer]

You may as well attach it to a rock.

Which would be my office, and quite interesting, given 'time'.

Anyhoo … what speed would the aircraft be going when it is in 'formation' with the props? Any particular difficulties in going 'slow' (as I imagine it is)?