Ask The Pilot

[jb747]

An aerodynamic question:

What is the practical difference between a stiff wing and a wing with less rigidity.

Seems like the B787 has a 'flexible" wing.

I expect it's more an engineering question than aerodynamic. A more flexible wing will give a better ride, but that's about all I can think of in its favour.

 

[jb747]

Are the spares so expensive that it is cheaper for them to be carried on board (with a fuel and weight penalty) than stored on the grounds at certain airports?

Most items relating to aircraft are extremely expensive. Like everything, there would have been an analysis done of the cost vs value, and the end result is that a small spares package is carried on most aircraft. As to just what it contains, I have no idea....

 

[harvyk]

I expect it's more an engineering question than aerodynamic. A more flexible wing will give a better ride, but that's about all I can think of in its favour.

It has more to do with ridged structure are more likely to break than structures with some give.
Ridged structures can be very brittle and don't handle changing stresses very well.

 

[Awesom Andy]

Most items relating to aircraft are extremely expensive. Like everything, there would have been an analysis done of the cost vs value, and the end result is that a small spares package is carried on most aircraft. As to just what it contains, I have no idea....

I think it also caters for the times when the aircraft is diverted, and needed spare parts. Say, if the aircraft couldn't land in LHR, and diverted to AMS, and then you needed a part.

 

[Dale Eastham]

Do a search for "youtube aircraft departure from controlled flight". The F22 is a doozy.

Watched this video last night - that is one savage departure alright (the audio makes it even better).
Theres an equally scary equivalent in an F-18 I found in the list below that one, if only due to the altitude it happened/ was carried out at.

 

[Melburnian1]

...Sadly, the driving standard is slowly being applied to flying...

It is hard to objectively judge as there is a danger of 'rose tinted glasses' appearing in musing about 'how it was better 20 years ago' but friends also comment to me in a similar vein re the roads and driving skills.

As aviation continues to expand within and to/from nations such as mainland China, apart from the 'poaching' of Westerners as flight crew by offering attractive packages, are airlines in those sorts of countries employing Westerners (or engaging them on contracts) to act as check captains and other supervisory roles, or do they tend to have a preference to promote from their own nationality's ranks?

Does nationalism or zenophobia come into this despite many nations having purchased Airbuses or Boeing planes?

Is engaging experienced Westerners, some of whom may have come up through flying for the RAF/ RAAF and so on a reasonable way to try to ensure that those flying internationally are extremely competent, rather than the oppsoite that was implied in the above comment?

 

[jb747]

It is hard to objectively judge as there is a danger of 'rose tinted glasses' appearing in musing about 'how it was better 20 years ago' but friends also comment to me in a similar vein re the roads and driving skills.

My rose tinted glasses tell me that in the past pilots pretty well always had substantial pre airline experience. Whether that was in the military, or GA, doesn't matter all that much. Cadets existed, but even they were normally pushed out to GA to gain experience before being allowed into the airliners.

Now, we have people with minimal time going straight into the right hand set of large aircraft. This will work to a degree, especially as those aircraft do tend to be very reliable. But, you don't have to look very far to find multiple examples of people who simply could not fly (Air Asia, AF447, Colgan, Asiana). These are the tip of the iceberg.

Now, I'm not saying they're all like that, but if it becomes more difficult to fill slots, the easiest way is to simply lower the bar. So, perhaps the odds start to increase. Of course, you don't have to be a foreign airline for this to be appealing.

As aviation continues to expand within and to/from nations such as mainland China, apart from the 'poaching' of Westerners as flight crew by offering attractive packages, are airlines in those sorts of countries employing Westerners (or engaging them on contracts) to act as check captains and other supervisory roles, or do they tend to have a preference to promote from their own nationality's ranks?

They may hire sim instructors from overseas. Supervisory people will be home grown. The numbers are a tiny proportion in any event, and won't make a difference either way.

Is engaging experienced Westerners, some of whom may have come up through flying for the RAF/ RAAF and so on a reasonable way to try to ensure that those flying internationally are extremely competent, rather than the oppsoite that was implied in the above comment?

Having a smattering of foreign ex military pilots does nothing for the overall competency of the airline. You need a comprehensive training and checking system, that vigorously weeds out those who can't, and ensures those who can, are properly trained. A visual approach should offer no difficulty at all, nor should a simple law reversion, but we've seen both of these take down aircraft in the last couple of years. From what I've heard from some of my friends who have flown overseas, the standard of training/checking can even vary depending upon whether you're a local or foreigner, with the locals avoiding the rough end.

Westerners aren't the only people who can fly, and you'll note that the examples I gave above included two western airlines. It's the attitude of the management that is the most important part of this equation, and whilst EVERYBODY, without exception, claims that safety is their first priority, my reading of the situation is that it comes a long way after any financial issues.

 

[Major]

Incident: Jazz CRJ9 enroute on Dec 19th 2016, loss of 40 knots and about 800 feet

After this particular incident the aircraft was required to have a service inspection. Why would that be so ?

Do all aircraft require an inspection after severe turbulence ?

 

[Saab34]

Noticed the other day in an Airbus (Straight in approach 16 Melbourne) the pilot dropped the gear before depoloying flaps. What would be the reasons for gear early in most cases?

 

[Boris spatsky]

Incident: Jazz CRJ9 enroute on Dec 19th 2016, loss of 40 knots and about 800 feet

After this particular incident the aircraft was required to have a service inspection. Why would that be so ?

Do all aircraft require an inspection after severe turbulence ?

Severe turbulence can place aerodynamic loads on the aircraft that are outside the normal design specs - every aircraft i have flown has required an engineering inspection after any severe turb event (or suspected, as determined by the pilot in command).

 

[Boris spatsky]

Noticed the other day in an Airbus (Straight in approach 16 Melbourne) the pilot dropped the gear before depoloying flaps. What would be the reasons for gear early in most cases?

High energy state (fast or high on profile or both) can lead to gear being selected earlier than normal (gear normally has a higher limiting airspeed than slats/flaps so you can select it earlier if you really need to.) I can't speak for Airbus but i assume it is similar.

 

[jb747]

Noticed the other day in an Airbus (Straight in approach 16 Melbourne) the pilot dropped the gear before depoloying flaps. What would be the reasons for gear early in most cases?

At lower speeds, the speed brakes are relatively ineffective. The landing gear on the other hand, is extremely draggy, and will kill energy very rapidly.

The normal sequence is to take the first couple of stages of flap (1 & 2 AB, 1 & 5 Boeing) before the gear. These early stages are leading edge (slats/flaps), and area increasing flaps at the rear. There's very little drag in them. The final flap stages have plenty of drag, but that also goes with restrictive speed limits, so if you're at all high energy, you may not be able to get them out.

If you intercept the glideslope a bit fast, even with the first two stages out, the 380 will just drift down the g/s without any deceleration. You'll need the gear for the drag.

The leading edge devices aren't anywhere near as obvious when extended as the trailing edge, so they may have been out. But, if the energy state is high enough, gear first is a good solution.

 

[jb747]

Incident: Jazz CRJ9 enroute on Dec 19th 2016, loss of 40 knots and about 800 feet

After this particular incident the aircraft was required to have a service inspection. Why would that be so ?

Do all aircraft require an inspection after severe turbulence ?

Whilst, according to the media, 'air pockets' have aircraft falling thousands of feet as a matter of course, the reality is that there's no such thing. Aircraft, even in severe turbulence rarely deviate more that a few feet from their initial positions. So, this is immediately unusual, as there was a large height deviation. The loss of speed is probably a large contributing factor though, as it would be difficult to recover 40 knots whilst level at altitude...you simply won't have enough power.

Airliners normally have 'g' limits of about 2.5g. That means an 80 kg person would weigh 200 kgs. It also means that the wings are having to support an aircraft that suddenly weighs 2.5 times as much. Transient/dynamic loadings can be much higher, which is why control inputs should be slow and steady. For instance if I rapidly roll an aircraft, and simultaneously pull to the max g, one wing will achieve much higher g than the other. That loading will also vary along the span. This is called rolling g, and whilst the actual pulled load could be within the design limits, the loading hit at the extremities could be well over. The unevenness of the loading twists the structure. Whilst pilot inputs shouldn't cause rolling g issues, once the uncommanded effects of turbulence come in play, you can't really tell what the loads were, unless the aircraft is properly inspected.

Rapid control reversals, which could also be initiated in turbulence also have the potential to over-stress the structure. The A300 that crashed in NYC after the FO initiated a series of full rudder reversals is the best example of this. Utterly pointless flying technique BTW.

This, from an Australian registered ATR is another example of what can happen in turbulence. It's not that the turbulence, per se, was horrible, but it can start a chain of undesirable events.
ATSB reports on Virgin Australia ATR structural damage | Australian Aviation

and for more detail...
https://www.atsb.gov.au/publications/investigation_reports/2014/aair/ao-2014-032/

 

[Cheatah]

Perth alternates

JB

Catching up on some of the information around the proposed 787 service London>Perth direct. I see there have been some posts on AFF previously about alternates to Perth which I assume will remain for the proposed 787 service(Learmonth, possibly Pearce/Kalgoorlie)

I was reminded about a QF A330 incident into Perth back in 2006. Coming from Singapore it got caught out by unexpected Fog and had no choice but to land under the required visibility minimums as it had no fuel to go elsewhere. Its last chance to divert was the TOD which - to me as a passenger at least - seems earlier than I would have thought.

WHat would have happened if, during this a330 incident, or a future incident, Perth airport itself was closed not due to weather but due to an issue within the airport itself? Ie obstructed runway. I cant see where else this A330 could have gone. Maybe Pearce if it was available - no assurances.

Thoughts? Do you know how late the 787 flights will have to make a decision to divert? I thought all aircraft could circle around their intended destination for 30 mins before then diverting. Do you know if this will be the case for the proposed LHR>Per flights?

 

[clazman]

Re: Perth alternates

Would have thought Kalgoorlie would have been a option as well

 

[Cheatah]

Re: Perth alternates

Would have thought Kalgoorlie would have been a option as well

Maybe. However legally they didnt need to hold enough fuel to get to Kalgoorlie , given they declared a Mayday and went under legal minimums to get into Perth I wouldnt think Kalgoorlie was an option!

I didnt realise Australian carriers dont need to hold enough fuel to ensure they get to their destination, and divert to their alternate from there. It appears, on some flights at least, any divert decision needs to be made well before the aircraft arrives at the destination.

It will be interesting to see if the proposed LHR-PER services will be requried to have holding fuel over Perth, and suitable reserves to get to an alternate. If that alternate is Learmonth then that will add 2 hours flying time!

 

[clazman]

Re: Perth alternates

If that alternate is Learmonth then that will add 2 hours flying time!

Assuming the aircraft is already close to Perth, but depending on the route would be less than 2 hours to Learmonth.
Kalgoorlie is only a 55 minute flight from gate to gate, or RAAF Pearce
Something else to consider would be some of the mines in WA have decent fields that already take jets

 

[AviatorInsight]

Re: Perth alternates

I only have a couple of minutes before departure so I'll be brief, but it largely depends on the airline's fuel policy. Our (VA) policy is for any international ​flight to carry fuel for an alternate airport regardless of what the weather may be. Usually our last point of diversion will be prior to TOD to another airfield, should our destination and primary alternate become unserviceable.

 

[clazman]

Re: Perth alternates

TOD - top of descent?

 

[Cheatah]

Re: Perth alternates

I only have a couple of minutes before departure so I'll be brief, but it largely depends on the airline's fuel policy. Our (VA) policy is for any international ​flight to carry fuel for an alternate airport regardless of what the weather may be. Usually our last point of diversion will be prior to TOD to another airfield, should our destination and primary alternate become unserviceable.

Thanks Aviator. I guess my original surprise was the QF Singapore flight I mentioned earlier didnt carry any fuel for diversion to an alternate, and while the original forecast had no prediction of Fog plenty of other reasons could have caused the airfield to close. Particulary since Perths two runways intersect, completely possible an aircraft due to arrive immeidately before the QF flight became disabled and blocked both runways.

I get the point Clazman made about various mine sites have a long enough stretch of runway but if the aircraft is low on fuel, the last thing I think the pilots would want to do is having to quickly determine which minesite has a long enough runway, does it have lighting etc. Most certainly they wont have an ILS so given the foggy weather conditions I think most of those minesites within a short distance from Perth would have been unavailable anyway to the crew.

Will be interesting to see what improvements, if any, are made to Kalgoorlie airport to support the upcoming 787 operations.