Ask The Pilot

[jb747]

Hey JB, Just wondering if you have ever operated routes that were not daily but maybe once or twice a week on your type? If so, what was the process, just kill 3 days in X location?
Was just looking at CX and how they only fly 2 744 services a week from HKG to JNB now, meaning there is a 3-4 day gap between the when crew would have flown in the 2nd service for the week and when the 1st service of the next week would arrive from HKG for them to fly out on.
Is it normal that crew would just kill time for that period or would they be paxing back and forth and only taking a crew down the day before they have to fly the service back? (hope i structured that in a coherent enough way)

Long slips like that do happen. I recall that Zimbabwe was like that back when I did my one and only trip there. Generally a waste of time from everyones' perspective.

 

[jb747]

Has any A380 or 747 exceeded the sound barrier? Is this avoided when carrying a load of passengers?

Whilst there have been claims that one particular aircraft did so, I have my doubts. A 747 is fast (.92 is quite achievable), but the drag rise as you approach mach one is very steep. The A4, which was a much faster aircraft than the 747, needed a gravity assist and full power to become supersonic.

On the other hand, it is quite easy to have some of the local airflow become supersonic. That happens somewhat below mach one, and occurs because flows around the aircraft can be accelerated by its shape.

 

[Skyhigh777]

How is ground speed actually measured? From my understanding, pitot tubes measure airspeed. There'd have to be some reference point on the ground to measure ground speed right?

Thanks JB

 

[jb747]

The inertial reference system measures every acceleration. That is used to calculate groundspeed and position. The GPS also works out the same information.

Inertial navigation system - Wikipedia, the free encyclopedia

 

[Major]

At the gate what is the procedure in the coughpit just before push back and who gives the approval for ground staff to close the final door ?

 

[WheelieBagWanderer]

Hi JB,

Can you please sum-up in a quick paragraph (if possible) how modern aircraft navigate from A to B?

Last time I had this explained to me, which was a long time ago I have to admit, it seemed to be via a series of way-points and beacons and distances were measured "abeam" to a particular point.

Has GPS taken over aircraft navigation now, or do you still use radio beacons and waypoints? Or GPS to guide yourself to waypoints?

I guess in a way I'm asking how the increase in prevalence of GPS has influenced aircraft navigation in recent times. In the case of older aircraft such as Qantas' 767 fleet, would the navigation used on these aircraft be the same as when they were first in service, or have the navigation systems been "upgraded" somehow?

Thanks in advance if you can explain a little bit as to how it works. This part of aviation has always fascinated me and a small idea of how it works would be wonderful. Cheers!

 

[flychrisfly]

Hi JB

after landing which items of airplane configuration are returned or reset to "zero"?

Obviously, the gear is left extended but I notice the flaps and slats are retracted. Is that it?

 

[legroom]

Hi JB

I am aware that you have posted in the SQ thread but wish to put this Q here, if possible.

Is there any active monitoring of cabin air pressure and/or O2 content on a modern airplane ?

In other words, could there be a situation where cabin pressure and/or O2 content falls below acceptable threshold without crews' knowledge ?

Say, plane is on autopilot and the pilots are having a quick shut eye when that happens and everyone just drifts off into "deep" sleep.

Thanks for sharing your knowledge.

 

[Fruitcake]

Following on from the MEL discussion in the SQ diversion thread - what does the maintenance release document I use in a GA aircraft look like in your world? Is it supplanted entirely by the airline/aircraft's electronic record keeping systems or is there still a form of physical maintenance release used? Thanks!

 

[alieninperth]

like what happened here? Helios Airways Flight 522 - Wikipedia, the free encyclopedia

 

[jb747]

At the gate what is the procedure in the coughpit just before push back and who gives the approval for ground staff to close the final door ?

Just prior to push...wait for the ACARS load sheet, then get ATC approval for the push. Then complete the before start checklist, and you're ready to go.

The cabin crew ask for permission from the coughpit before closing the final door.

 

[jb747]

Can you please sum-up in a quick paragraph (if possible) how modern aircraft navigate from A to B?

Last time I had this explained to me, which was a long time ago I have to admit, it seemed to be via a series of way-points and beacons and distances were measured "abeam" to a particular point.

Has GPS taken over aircraft navigation now, or do you still use radio beacons and waypoints? Or GPS to guide yourself to waypoints?

I guess in a way I'm asking how the increase in prevalence of GPS has influenced aircraft navigation in recent times. In the case of older aircraft such as Qantas' 767 fleet, would the navigation used on these aircraft be the same as when they were first in service, or have the navigation systems been "upgraded" somehow?

Thanks in advance if you can explain a little bit as to how it works. This part of aviation has always fascinated me and a small idea of how it works would be wonderful. Cheers!

Waypoints and routes probably haven't changed dramatically. The way the waypoints are defined has though. Whilst lat/longs have been used for ages to define IRS positions, once in the terminal area the fixes tended to be just that...bearings and distances from navigation aids. The IRS might have been used to actually go there, but the aids were constantly being checked to ensure things stayed accurate.

GPS has enabled the creation of waypoints that aren't tied to ground based navigation aids. Generally it's described as RNAV. Approaches are even flown using RNAV (through the FMC) that emulate the tracks of VOR or NDB approaches, but with close to the accuracy of the precision aids (ILS). The older aids basically won't be with us much longer...

The 767 fleet came with twin ADF (for NDB navigation), twin VOR/DME, triple ILS/DME, and triple FMCs. When I left the fleet, some had a single GPS as well, but I think they now all have a twin installation. The other stuff is still there too. The 747-400 got twin GPS about ten years ago. A380 is similar.

 

[jb747]

Following on from the MEL discussion in the SQ diversion thread - what does the maintenance release document I use in a GA aircraft look like in your world? Is it supplanted entirely by the airline/aircraft's electronic record keeping systems or is there still a form of physical maintenance release used? Thanks!

Still a book full of paper chits. Electronic came with the A380, but it was terrible, and we've abandoned it.

 

[jb747]

Is there any active monitoring of cabin air pressure and/or O2 content on a modern airplane ?

Cabin altitude is constantly displayed. It's also tied in with the warning system. O2 content isn't. Basically the cabin air is just air grabbed from outside and given a bit of a squeeze.

In other words, could there be a situation where cabin pressure and/or O2 content falls below acceptable threshold without crews' knowledge ?

It shouldn't happen, but it certainly has. Some instances have been associated with faulty warning systems, whilst at other times the crew seem to have disregarded the warnings. Of course part of the issue with hypoxia is that people become confused as they become hypoxic. Probably the most dangerous form of depressurisation isn't the rapid one, but the slow and insidious. Couple that with a warning system that has issues, or that is set for a high altitude, and the crew could well be hypoxic before any warning occurs.

Not all aircraft are pressurised to breathable levels either. Fighter pilots don't wear the masks to look cool, but rather because their cabins are normally only notionally pressurised.

Say, plane is on autopilot and the pilots are having a quick shut eye when that happens and everyone just drifts off into "deep" sleep.

They aren't supposed to be having a shut eye at the same time! Nevertheless that seems to have been the outcome many times...especially with regard to business jets (Payne Stewart for instance).

 

[Flying Fox]

Another thread has an article about the retirement of a DC9 fleet with an average of 35 Yrs.

If an aircraft is maintained according to the book, could it keep flying indefinately? Or does the actual airframe get too old to safely fly and as a pilot, do you get concerned flying these old airframes?

Thanks

 

[jb747]

like what happened here? Helios Airways Flight 522 - Wikipedia, the free encyclopedia

Effectively, they took off with the pressurisation turned off. The packs were on, but because the outflow valve was open, it was just venting all of the air to the outside. The cabin may have been marginally pressurised, but not to any extent.

As they climbed, so did the cabin. When the first warning went off, the crew decided it was for something else (Boeing actually used the same noise for different things, but that shouldn't matter...you don't use the noise to differentiate). They continued the climb. By this stage I expect some of the first effects (of hypoxia) were already evident, and affecting all of their actions.

At any point up to the stage where both pilots collapsed, donning a mask would have quickly resolved the issue.

I suspect that it wasn't coincidence that the steward was able to enter the coughpit just as the engines flamed out. Lack of normal electricity possibly unlocked the coughpit door.

 

[jb747]

Another thread has an article about the retirement of a DC9 fleet with an average of 35 Yrs.

If an aircraft is maintained according to the book, could it keep flying indefinately? Or does the actual airframe get too old to safely fly and as a pilot, do you get concerned flying these old airframes?

They're a bit like your old favourite shoes. Replaced the uppers twice, and the soles three times, but still the same shoes.

Looked after properly age isn't an issue at all. Cycles is what wears an aircraft out...so a 10 year old 767 used by long haul is very likely in much better condition than the same aircraft used for short haul.

I've not seen any real difference in the reliability of new versus older aircraft. The old stuff settles down, and the new invents new problems.

The makers nominate some limits for the cycles and hours an aircraft can fly, but beyond that, it's most likely a trade off of the cost of maintenance and the availability of spares.

 

[legroom]

.... Probably the most dangerous form of depressurisation isn't the rapid one, but the slow and insidious. Couple that with a warning system that has issues, or that is set for a high altitude, and the crew could well be hypoxic before any warning occurs....

What would be the most optimal defense against this scenario [the slow and insidious depressurisation] ?

Keep your eyes peeled to the altimeter every 3-4 min ?

Thanks

 

[jb747]

What would be the most optimal defense against this scenario [the slow and insidious depressurisation] ?

Keep your eyes peeled to the altimeter every 3-4 min ?

If you're trying to defend against a warning system that doesn't work, then the only real defence would be to wear a mask at all times. But, really, we're just as reliant on those warning systems for everything (i.e. smoke, fire, etc). They're generally duplicated in some way, so as long as you actually respond to the warning, and don't sit and wonder what it means, you shouldn't have too many issues.

Being surrounded by information numbs you to it. A warning system will pick out the changes better than a person can.

Worth remembering that the 'time of useful consciousness' at FL400 is measured in seconds.

 

[WheelieBagWanderer]

Thanks very much for the answer on my navigation question, JB.

Another quick one if I may... I came across this photo on Twitter. https://twitter.com/coughpitChatter/status/419396421901484032/photo/1/large

It's pretty obviously what's wrong in that photo! Wouldn't there be some notification on the flight deck that the 1R door handle is in that position? Would this pose any issue for the aircraft in flight? I'm assuming not as there obviously hasn't been anything in the news about a mishap with this airline, but I was just curious. I've never seen anything like that before!

(The second thing that's curious about that photo is the FO wearing a Santa hat - I think! - but, whatever rubs your rhubarb I guess!)