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hkhoanguyen

Taxiing out with #2 and #4 - 748

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1 hour ago, PATCO LCH said:

But if you do a two engine taxi I was wondering if you wait until all engines are started ( at the runway I assume ) before the after start check list and TO flaps are set ? Wonder what the RW procedure is.

I don't do a two-engine taxi for Take Off purposes as the Button Version clearly states Start Sequence 4-3-2-1 and I just follow the Button prompts and ask the FO to start all four engines as per sequence. The Flaps 20 setting call comes in the Before Taxi Procedure.

RW, now that would be interesting but as Bryan at FS2Crew did have a r/w pilot doing his testing, I am fairly assuming that it is RW too, but hey,I could be way off beam😎

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3 minutes ago, vc10man said:

I don't do a two-engine taxi for Take Off purposes as the Button Version clearly states Start Sequence 4-3-2-1 and I just follow the Button prompts and ask the FO to start all four engines as per sequence. The Flaps 20 setting call comes in the Before Taxi Procedure.

RW, now that would be interesting but as Bryan at FS2Crew did have a r/w pilot doing his testing, I am fairly assuming that it is RW too, but hey,I could be way off beam

2 engine taxi is usually only after landing, as is simulated by FS2CREW. BA does this very diligently 

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Yours truly
Boaz Fraizer
Copenhagen, Denmark

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33 minutes ago, windshearDK said:

2 engine taxi is usually only after landing, as is simulated by FS2CREW. BA does this very diligently 

Yeah, you mentioned that to me this morning or afternoon, I think. So, my previous reply was dealing with checklists as logically, there would be no checklist if taxiing after landing except the shutdown procedure checklist, if I am not mistaken.

Again I've learned something off you re:BA, my ex-employer.

EDIT: Well, well, have just watched that Rampie-shot video and my eyes have been truly opened. Never knew that was allowed/possible on taxi-outs. So, for merely re-positioning an aircraft then this procedure seems okay it appears to me.

A real jerky video probably shot from a mobile phone as it seemed to lose focus quite often.

Edited by vc10man
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Unfortunately, it seems there are some rather suspect statements being made here about what happens in the real world. 

It is not normal practice to taxy out on only two engines In a B744; although I accept it is possible to do so at very light weights and some operators may do so in the -8.  However, I am currently not aware of any airlines that actually do this.

There are several good reasons why all four engines are used to taxy out for takeoff.  For example, at typical takeoff weights there is always a considerable risk of blast damage behind the aircraft when too much power is applied.  It is inevitable that excess thrust would be required to start taxying at high gross weights with only two engines running. Secondly, when taxying out for take off the core of all four engines need to warm up and all of the aircraft's systems need to be configured and checked before takeoff; this cannot  be achieved properly with only two engines running.  Even when there is a need to taxy the aircraft to a remote holding point it is standard practice to taxy using all four engines and carry out the pre-takeoff checklist as normal, but leaving the APU running.  At the remote holding point the engines are then shut down until the aircraft is cleared to re-start (using the APU as normal) prior to taxying for departure. 

After landing it is also normal practice in the B744 for only Engine #3 to be shut down, but only when it is safe to do so and after at least a one minute cooling down period with this engine running at idle thrust.  This helps to protect the engine from thermal shock, reduce brake wear, improve overall fuel economy and it also assists in reducing the aircraft's taxy speed at the much lighter landing weights.

I believe PMDG's B747 Queen of the Skies and the new B747/-8 handling procedures and checklists are meant to be generic, so if I am correct about this they are not meant to be representative of any specific Boeing aircraft operator.  Therefore, we should not be at all surprised if these items differ between these two aircraft types and the real world, as well as between all the other Boeing aircraft types PMDG models.      

Edited by berts
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10 hours ago, windshearDK said:

Another pilot friend of mine flies the 77W/77L and 77F and he didn't know that you have to do step climbs using vnav or FL/CHG as it helps to prevent icing in the fuel systems. This was a Boeing decree even after they updated the fuel filter because of the crash investigation conclusions in the BA crash at LHR where a 772 flamed out on final app. 

This is another suspect statement allegedly by your pilot friend, although you are quite right about the redesign of the filter following the unfortunate B777 accident due to fuel icing at LHR (fortunately nobody was killed) .

Step climbs usually have very little to do with preventing icing in the fuel systems, but everything to do with improving fuel economy and aircraft operating efficiency.  The risk of icing in the fuel system depends primarily on the outside air temperature that the aircraft is flying through and the amount of time it is there, the freeze point of the fuel and the actual amount of water content within it. 

The crew will know what the freeze point of their fuel is (-40C or -47C) and they should monitor the fuel temperature (i.e. Total Air Temperature) throughout the flight; especially during longhaul operations over Siberia in winter where 'Cold Soak' is most likely to occur.  When the B744's fuel temperature is less than -37C the EICAS advisory '>FUEL TEMP LOW' will be displayed and they must monitor it closely; especially if it gets anywhere close to +3C above the freeze point of the fuel, because fuel waxing will probably become an issue if they don't do something about it. The crew's actions will usually entail a combination of flying faster to increase the aircraft's skin temperature and descending (usually) or climbing (rarely) into warmer air with the expectation this will be sufficient to warm up the remaining fuel. Sometimes even banking the aircraft gently left and right from time to time is enough to mix the fuel up and keep it warmer.

 

Edited by berts

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18 hours ago, windshearDK said:

but you don't have the same 4 hydraulic systems like in the T7... How do you then turn them on to prevent spill?

Correct, you have the Left and Right system, but with multiple pumps. You generally pressurize the right system first before pressurizing the left system. The procedure i am familiar with is:

1. Right Electric Demand pump to AUTO, make sure FAULT light extinguishes.

2.Switch center 1 and 2 electric primary pumps to ON. Center 2 FAULT light may stay illuminated due to load shedding.

3. Left Electric Demand pump to AUTO, again make sure FAULT light extinguishes

4. Switch Center 1 and 2 Air Demand pumps to AUTO and verify FAULT light extinguishes.

 

For shutdown it's exactly the other way round, depressurizing the right system last.


Regards,

Harm Swinkels

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Just tested the same situation as in the video, the PMDG 747-8 behaves the same. So the HYD 1 system must be pressurized by the demand pump by bleed air from either APU or Engine bleed, since HYD 1 demand pump is an air driven pump.

 

747-8-2and48bks0.png

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Regards,

Harm Swinkels

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At 5:03 in the video you see that he has the AUX pumps in SYS 1&4 ON. That is not representative of the picture above. FCOM also says that these are electrical and used for ground handling operations, of which this clearly is. The fact that he used 2 and 4 might come down to personal preference, specific company maintenance policy or even cycles on the No. 1 engine. Who knows, but with the AUX pumps on, the requirement of which engines to use becomes moot. He even has HYD SYS 2 pump switch to OFF. It also appears as if he is describing rotor bowing to the filmer. Interesting stuff...

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Xander Koote

All round aviation geek

1st Officer Boeing 777

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2 hours ago, xkoote said:

At 5:03 in the video you see that he has the AUX pumps in SYS 1&4 ON. That is not representative of the picture above. FCOM also says that these are electrical and used for ground handling operations, of which this clearly is. The fact that he used 2 and 4 might come down to personal preference, specific company maintenance policy or even cycles on the No. 1 engine. Who knows, but with the AUX pumps on, the requirement of which engines to use becomes moot. He even has HYD SYS 2 pump switch to OFF. It also appears as if he is describing rotor bowing to the filmer. Interesting stuff...

In the video i believe, during taxiing, the pumps are configured all in AUTO except HYD 3, which is set to OFF. AUX 1 and 4 were only on during the engine start, if i remember correctly from the video. The EICAS HYD synoptic shows the same as in my picture (around 5:26 in the video). So both AUX pumps are not running during movement of the aircraft (assuming it is taxiing under its own power.) 

Edited by Heffron

Regards,

Harm Swinkels

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18 hours ago, berts said:

Step climbs usually have very little to do with preventing icing in the fuel systems, but everything to do with improving fuel economy and aircraft operating efficiency.  The risk of icing in the fuel system depends primarily on the outside air temperature that the aircraft is flying through and the amount of time it is there, the freeze point of the fuel and the actual amount of water content within it. 

As I recall, the reason is that using VNAV or FL CH will result in greater thrust change than using VS. The higher fuel flow helps prevent ice crystals collecting in the fuel lines and filters.


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5 hours ago, kevinh said:

As I recall, the reason is that using VNAV or FL CH will result in greater thrust change than using VS. The higher fuel flow helps prevent ice crystals collecting in the fuel lines and filters.

Maybe so, but the real danger of climbing to a higher altitude is that you are more likely to be climbing into even colder air, so that when you level off and resume your normal cruising speed the potential fuel icing problem will not have gone away, but could possibly become far more serious in a shorter time period.  Normally the rate of cooling can be in the order of 3C per hour but in extreme conditions it has been known to be up to 12C per hour and it can take up to an hour for the fuel temperature to stabilise in warmer conditions.

Inflight conditions are of course different for every flight and so I accept this decision could involve a climb as you say if the air is known to be warmer higher up, but the fuel flow can also be increased by flying faster at the same or a lower altitude and the increase in speed should help to slow down the 'cold soak effect'.  Keeping an eye on the Total Air Temperature is key to anticipating the potential risk of the remaining fuel in the tanks starting to wax as ice crystals, which incidentally can occur below the freeze point of the fuel. Unfortunately, the amount of fuel reserves being carried these days is often the minimum required for the flight and this commercial pressure can sometimes have an adverse impact on the possible options available to the crew, i.e. deviating to a warmer air mass;  or descending and flying faster (which I suggest is normally the preferred option).   

Edited by berts

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8 hours ago, Heffron said:

In the video i believe, during taxiing, the pumps are configured all in AUTO except HYD 3, which is set to OFF. AUX 1 and 4 were only on during the engine start, if i remember correctly from the video. The EICAS HYD synoptic shows the same as in my picture (around 5:26 in the video). So both AUX pumps are not running during movement of the aircraft (assuming it is taxiing under its own power.) 

You're absolutely right. The AUX pumps were switched OFF


Xander Koote

All round aviation geek

1st Officer Boeing 777

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On 1/26/2019 at 11:15 PM, berts said:

This is another suspect statement allegedly by your pilot friend, although you are quite right about the redesign of the filter following the unfortunate B777 accident due to fuel icing at LHR (fortunately nobody was killed) .

Step climbs usually have very little to do with preventing icing in the fuel systems, but everything to do with improving fuel economy and aircraft operating efficiency.  The risk of icing in the fuel system depends primarily on the outside air temperature that the aircraft is flying through and the amount of time it is there, the freeze point of the fuel and the actual amount of water content within it. 

Guess there are things you don't know... Your choice of words are very very strange


Yours truly
Boaz Fraizer
Copenhagen, Denmark

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22 hours ago, Heffron said:

Correct, you have the Left and Right system, but with multiple pumps. You generally pressurize the right system first before pressurizing the left system. The procedure i am familiar with is:

1. Right Electric Demand pump to AUTO, make sure FAULT light extinguishes.

2.Switch center 1 and 2 electric primary pumps to ON. Center 2 FAULT light may stay illuminated due to load shedding.

3. Left Electric Demand pump to AUTO, again make sure FAULT light extinguishes

4. Switch Center 1 and 2 Air Demand pumps to AUTO and verify FAULT light extinguishes.

 

For shutdown it's exactly the other way round, depressurizing the right system last.

wow interesting thank you! But usually when you turn on the hydraulic systems you put 1 or 2 in AUX and not on... Is it the right to left logic with simply some in the AUX position


Yours truly
Boaz Fraizer
Copenhagen, Denmark

Boeing777_Banner_Pilot.jpg

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17 hours ago, kevinh said:

As I recall, the reason is that using VNAV or FL CH will result in greater thrust change than using VS. The higher fuel flow helps prevent ice crystals collecting in the fuel lines and filters.

This is exactly the reason! The high rise in fuel flow will ensure that the design of the fuel filter will be working 100%, its a small easy extra precaution.. It was mentioned by a Boeing personel in a documentary about the British Airways crash

Edited by windshearDK

Yours truly
Boaz Fraizer
Copenhagen, Denmark

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