Ask The Pilot

[straitman]

Given transponders are on, is there any technical reason re the aircraft or is it just a quirk of these useful but imperfect tracking sites?

I’ll go with the last one but someone may have some real insight.

 

[jb747]

There is no particular reason for the drop outs that I know of. The transponder is turned on just before push back, and off at shutdown. I expect the issue will be related to buildings blanking the transmitter.

 

[Quickstatus]

In a 2 engine, can 1 bleed air system provide sufficient cabin pressure? What if anti icing is also necessary?

In a 4 engine how many bleed air systems are necessary for this function?

Can the APU assist?

 

[jb747]

In a 2 engine, can 1 bleed air system provide sufficient cabin pressure? What if anti icing is also necessary?

Yes. There will generally be an altitude limitation if you are reduced to one bleed, but that has more to do with depressurisation requirements should the second one fail. Anti ice should not be an issue.

In a 4 engine how many bleed air systems are necessary for this function?

Two generally, though you'll turn the bleed flow to the packs off for approach, as you may want all of the power, and pressurisation isn't an issue at that stage. And if you're down to one engine, it isn't an issue at any stage.

Can the APU assist?

Yes, though the APU isn't available on all aircraft at all times. On the 747 it cannot be started in flight, and on the 380 only below FL200. The twins can start it at any time.

 

[Quickstatus]

How much power is bled off by bleed air?

 

[jb747]

How much power is bled off by bleed air?

About 2%.

 

[D747]

Yes, though the APU isn't available on all aircraft at all times. On the 747 it cannot be started in flight, and on the 380 only below FL200. The twins can start it at any time.

Do all airliners have RATs? What are the reasons for APUs to have different operational abilities?

 

[jb747]

Do all airliners have RATs?

No. The A380 has one that will provide emergency electrics (about 10% of the normal load), but nothing else. The 747 has no RAT. The 767 had one that that provided emergency flight control hydraulics only. 787 has its lithium battery pack. It varies according to the need, i.e. the ability of the APU and other systems to provide the minimum necessary electrics and hydraulics for flight.

What are the reasons for APUs to have different operational abilities?

Again need. The twins will regain most of their capability (except thrust) if you start the APU after an engine failure. In the quads a single failure doesn't matter all that much, so they are either restricted or cannot be used at all.

 

[D747]

No. The A380 has one that will provide emergency electrics (about 10% of the normal load), but nothing else. The 747 has no RAT. The 767 had one that that provided emergency flight control hydraulics only. 787 has its lithium battery pack. It varies according to the need, i.e. the ability of the APU and other systems to provide the minimum necessary electrics and hydraulics for flight.

Again need. The twins will regain most of their capability (except thrust) if you start the APU after an engine failure. In the quads a single failure doesn't matter all that much, so they are either restricted or cannot be used at all.

Thank you very much JB.

 

[andmiz]

The newer 747 also has a RAT.

 

[lastrow]

Please tell me what is a RAT , sensible answers only please.

 

[Hvr]

Please tell me what is a RAT , sensible answers only please.

I used my mouse to google it and found this:

Ram air turbine - Wikipedia
A ram air turbine (RAT) is a small wind turbine that is connected to a hydraulic pump, or electrical generator, installed in an aircraft and used as a power source. The RAT generates power from the airstream by ram pressure due to the speed of the aircraft.

 

[AviatorInsight]

Looks like that. The RAT is used as an emergency source of power. Deployed automatically on the 777 when all other sources of power are not available. Will provide very basic instrumentation and hydraulic systems. Basically only enough to get you onto the ground.

 

[Mogul]

Very quick Mel to Sydney flight last night to beat curfew. From wheels up to wheels down 50 minutes. No cruise power was on all the way, it didn't seem to back off much during the descent either.

 

[Himeno]

View attachment 132284

Looks like that. The RAT is used as an emergency source of power. Deployed automatically on the 777 when all other sources of power are not available. Will provide very basic instrumentation and hydraulic systems. Basically only enough to get you onto the ground.

There is an episode of Ultimate Airport Dubai where they deploy the RAT on an EK A380 for maintenance.

 

[lastrow]

Thanks for those replies. Very good thinking - using a mouse to catch a RAT. I have often seen these turbines more like windmills.They must spin at a very high rate at aircraft speed although when loaded up the rate would be slower. These must be very old devices , I seem to remember seeing them attached to pre war planes although they might have been used to simply measure speed.

 

[straitman]

Thanks for the extra input folks as it is appreciated.

However a reminder from post #1 that it is not a discussion thread and is for pilots and ATC type people to answer questions about aviation.

As this is an "ask the pilot" thread, we ask that non-pilot members refrain from answering questions that have been directed to pilots until the pilots members have had a good opportunity to answer the question (i.e. at least 7 days). Posts contrary to this request or discussions that get too far off topic may be removed or moved to a more appropriate thread or forum so we can retain order and respect in this thread.

We appreciate your understanding.

 

[Melburnian1]

With Oz's main domestic and international airports, there are 'big ticket' items that should improve operations - such as new runways.

There are also smaller scale annoyances that delay flights, such as passengers who dawdle and aren't at the gate when boarding is about to close. They're not the fault of deficient airport infrastructure.

What one smaller thing, if any, would our aviators suggest that could improve timekeeping at particular airports in Australia and to what airports does it apply?

 

[AviatorInsight]

Very quick Mel to Sydney flight last night to beat curfew. From wheels up to wheels down 50 minutes. No cruise power was on all the way, it didn't seem to back off much during the descent either.

More than likely would have had cruise power set but if you're beating curfew then my assumptions are:

1) You flew at a lower altitude to pick up the higher TAS (therefore it's noisier and the sense of full thrust from the cabin?)

2) Same sort of situation happening on descent (most descents are planned on an idle thrust descent but again at a high speed = more noise and a faster rate of descent giving the sensation of thrust being put on)

 

[AviatorInsight]

With Oz's main domestic and international airports, there are 'big ticket' items that should improve operations - such as new runways.

There are also smaller scale annoyances that delay flights, such as passengers who dawdle and aren't at the gate when boarding is about to close. They're not the fault of deficient airport infrastructure.

What one smaller thing, if any, would our aviators suggest that could improve timekeeping at particular airports in Australia and to what airports does it apply?

Just one??

I would say get rid of the hourly cap at SYD. Many a time we have pushed back on time only to be delayed 10mins at the holding point because the cap had been reached for that 15min block. So we were burning fuel and time just waiting only to burn more fuel to make up time at the other end and avoid being late.