hkhoanguyen

Taxiing out with #2 and #4 - 748

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Hi, 

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In this video, I don't understand why they started pushing back and taxiing with only #2 and #4 ? as far as I know, #2 and #4 both provide breaking (normal and alternate) but only #1 provide nose and body steering, #2 does not, how could they steer the plane without ENG #1 ?

Someone could explain me ?

Thanks

Edited by hkhoanguyen

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I think they had HYD 1 on the electrically powered AUX pump, which provides hydraulic pressure without ENG 1 running.

 

EDIT: I actually watched the video now, so my initial reply is kind of false i guess. I guess the #1 Demand Pump is running on bleed air from either the APU or the 2 running engines. 

Edited by Heffron
actually watched quoted video.

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From a real world 744 and 748 pilot he told me that they always taxi using #1 and #4 due to hydraulics etc. here's what he wrote me:

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"“On two engines it’s always the outer 2 (#1 & #4) [that are running] because nose and body gear steering are on hydraulic system 1 and primary brakes are on system 4”

When asking about the -8 he said:

 

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"Same deal. Systems are very similar on the -8”"

I think the PMDG is a bit wobblier to taxi if I taxi on #2 and #3

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Great heads up. One question though, can you ask your 744 and 748 friend, when exactly do they start #2 and #3? During the taxi, or nearing the threshold, because it does take a while to spool-up?

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But the questions remain, why did they start 2 and 4 instead of 1 and 4? And how is the HYD 1 system being pressurized if eng #1 is not running.

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17 minutes ago, vc10man said:

Great heads up. One question though, can you ask your 744 and 748 friend, when exactly do they start #2 and #3? During the taxi, or nearing the threshold, because it does take a while to spool-up?

Mostly 2 engine taxi is from after landing until the parking position/gate... The instance he was talking about was from parking to deicing... I guess they turn them on as soon as the deicing has been completed

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7 minutes ago, Heffron said:

But the questions remain, why did they start 2 and 4 instead of 1 and 4? And how is the HYD 1 system being pressurized if eng #1 is not running.

Yeah someone sent me that video also asking why... I don't know why. The answers I got was from a pilot flying for Atlas Air Cargo... So various airlines could have different procedures, but the reasoning behind the procedure my friend does is solid I would say... Don't really have to understand why people do things differently.

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.

There are also some 777 pilots that are not aware of the technique of turning on the HYD on the 777 to prevent spill over...

When the logic behind a procedure fits the systems of the aircraft I tend to favor that procedure over what others might or might not do...

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Great answers, Boaz. You never stop learning in this Forum even if you are an experienced simmer.

Just as I am watching a very instructive real-world ex-Airtours 757-200 from EGCC-Dalaman. So much know-how to glean there that can then be applied to the cs757-200v3

Edited by vc10man
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2 minutes ago, vc10man said:

Great answers, Boaz. You never stop learning in this Forum even if you are an experienced simmer.

And in real life! I learn a lot from my friends but sometimes I can teach them a little too! That's why I love aviation! Always more learning to do!

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18 minutes ago, windshearDK said:

And in real life! I learn a lot from my friends but sometimes I can teach them a little too! That's why I love aviation! Always more learning to do!

👍👍

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1 hour ago, windshearDK said:

There are also some 777 pilots that are not aware of the technique of turning on the HYD on the 777 to prevent spill over...

Also applies to the 747. Pressurize #4 first and depressurize last to prevent fluid transfer between systems. 

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Do you do the before taxi check list before taxi or after all engines are started in which case it would be the after start check list? I know that sounds like a nonsensical question but being an FS2 Crew user it has left me wondering. Also same question applies to setting TO flaps.(In non icing conditions)? 

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I use FS2Crew too, and using only the Button Version, but I have no issues with the Before Taxi Checklist, as well as it being available in the 747-8i checklists

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2 hours ago, vc10man said:

I use FS2Crew too, and using only the Button Version, but I have no issues with the Before Taxi Checklist, as well as it being available in the 747-8i checklists

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.

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3 hours ago, Heffron said:

Also applies to the 747. Pressurize #4 first and depressurize last to prevent fluid transfer between systems

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

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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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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.

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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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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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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

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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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