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19AB67

Pressurize only one system first...

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Hi captains, 

 

in my thread on the upcoming DC6 tutorials I mused about learning in the PMDG tutorials nicely when and why we have to do what. 

http://www.avsim.com/topic/485979-dc6-tutorial/

 

One of these was for NGX -- if I haven't dreamt it -- that

   after switching on the beacon

       before push back

*only* HYD DEMAND PUMP ELEC1 (the right one next to ENG2) is switched on... 

 

if I remember correctly, because this does *not* pressurize the front wheel steering: 

As long as push back is not completed moving the tiller could injure the rampies. 

 

1. pdf tutorial 1 does not mentioning switch them on at all, I thing in order not to overload the newbie. 

2. pdf tutorial 2 reads on page 78 'Turn the ELEC 1 and 2 hydraulic pumps on.' 

3. Hah! FCOM1 reads on page 106: 

 

   Hydraulic panel.................................................................Set F/O

 

   If pushback is needed and the nose gear steering lockout pin is not installed:

   WARNING:Do not pressurize hydraulic system A.

      Unwanted tow bar movement can occur.

 

   System A HYDRAULIC PUMP switches – OFF

      Verify that the system A pump LOW PRESSURE lights are illuminated.

   System B electric HYDRAULIC PUMP switch – ON

      Verify that the system B electric pump LOW PRESSURE light is extinguished.

 

Well, there is still a condition: If pushback AND nose gear steering lockout pin is not installed...

Page 107 reads: 

   If pushback is not needed, or if pushback is needed and the nose gear steering lockout pin is installed:

      Electric HYDRAULIC PUMP switches – ON

 

Therefore in the pushback dialogue: 'We are watching for the pin...', 

means if the tug driver hold up the pin with the flag on it, the crew knows that now the steering will work. 

 

Simalar for the T7: 

   BEFORE START:
    Turn on the hydraulic pump switches in the following order:
    R ELEC DEMAND (FCOMv1: This one first to prevent fluid transfer between systems.')
    C1 and C2 ELEC PRIMARY
    L ELEC DEMAND
    C1 and C2 AIR DEMAND

 

All can and shall be switched on at once in the described sequence. 

 

Well, I learnt something... and I have to read more carefully the whole section on one topic... 

 

How do I know that the nose gear steering is locked out? Because of my walk around? 

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*only* HYD DEMAND PUMP ELEC1 (the right one next to ENG2) is switched on... 
 
if I remember correctly, because this does *not* pressurize the front wheel steering: 
As long as push back is not completed moving the tiller could injure the rampies. 

 

Some operators do this. It's usually those who operated the 73 prior to the lockout pin was available (731/732, I think), and is a little bit of overkill in my eyes. On the ramp, we never hooked up a towbar and let it just sit there. We hooked it up and then within a minute or so brought a tug up to it. So, sure, in that minute, you're exposed if the lockout pin somehow failed, but that's pretty unlikely. Rampies were also taught to not be anywhere near it if it wasn't absolutely necessary.

 

 

 


How do I know that the nose gear steering is locked out?

 

You'd see the gear pin inserted.

 

 

 


Because of my walk around? 

 

Yep.

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How do I know that the nose gear steering is locked out? Because of my walk around?

 

 

Correct, you'll either see it inserted or the ground crew will tell you it's inserted (remember on the 747 v1 by PMDG; the pushback dialogue included a "confirm pin is inserted/removed" line)

 

This is how it looks:

b737-ng-landing-gear-39-638.jpg?cb=14437

 

EDIT: Kyle was faster again! (I'm not doing this on purpose, I promise :)

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Thanx, Kyle. 

 

 

 


On the ramp, we never hooked up a towbar and let it just sit there. We hooked it up and then within a minute or so brought a tug up to it.

 

Well, before boarding at EDDT/TXL I often see the tow bar being hooked up, but no tug available for ages... 

(Tscha, when will EDDB/BER open finally? A laughingstock -- Lachnummer, ger. -- the German Gruendlichkeit...) 

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Well, before boarding at EDDT/TXL I often see the tow bar being hooked up, but no tug available for ages... 

 

Again, with the pin in, that thing isn't moving anywhere. Most aircraft have lockout pins now. We would occasionally do the same if we were short on tugs and/or staff. That way, when the tug rolled up, it was a quick connect and go. Still, while it was attached, you stayed away from it just in case the stars magically aligned and the lockout pin didn't actually lock things out for some reason.

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Again, with the pin in, that thing isn't moving anywhere.

 

Yup, got it. Thanx. 

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So question, even if the lockout pin failed, why would the gear flap about if it is aligned head-on and the crew don't touch the tiller?

 

That said, stranger things have happened.

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if the lockout pin failed, why would the gear flap about

 

Well it wouldn't flap around like a flag, it just wouldn't be locked and it could eventually inadvertently move, bend and/or break the tow bar or even worse, hurt somebody happening to be around.

 

Also nobody will guarantee that none of the pilots will not rest their hand on the tiller, or otherwise touch it, which they shouldn't anyway, but they could.

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why would the gear flap about if it is aligned head-on and the crew don't touch the tiller?

 

In addition to what Jaime said above, the other scenario is that during pushback if the pin is not inserted (or not inserted correctly) and the NWS becomes pressurised you will then have a couple of thousand PSI of hydraulic pressure trying to centre the nose wheel against the tug, most likely resulting in damaged equipment (towbar/tug/nosewheel) but possibly injury as well.

 

Not sure about the 737, but I do remember reading about a couple of incidents on the 747 where the pin fell out during pushback resulting in this happening (I think there was an issue with the design of the pin and also the fact that they were very similar, but not identical to, the pin from another type -- and you can guess what happened). Whether it was ever fixed I don't know.

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Not sure about the 737, but I do remember reading about a couple of incidents on the 747 where the pin fell out during pushback resulting in this happening (I think there was an issue with the design of the pin and also the fact that they were very similar, but not identical to, the pin from another type -- and you can guess what happened). Whether it was ever fixed I don't know.

 

74 pin is similar to the 75 pin, I believe, but they are not interchangeable.

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Do the tug drivers have all sorts of pins on board of their tug? 

Edited by 19AB67

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The 747 Pin has locking balls in the middle of pin to hold it in place.   The 757 pin just happens to be the same size but the locking balls are on the end of the pin.  Needless to say they aren't interchangeable and bad things happen when you use a 757 pin in a 747.  Very likely a contributing factor in the recent "Ed force One" incident in Brazil.

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In addition to what Jaime said above, the other scenario is that during pushback if the pin is not inserted (or not inserted correctly) and the NWS becomes pressurised you will then have a couple of thousand PSI of hydraulic pressure trying to centre the nose wheel against the tug, most likely resulting in damaged equipment (towbar/tug/nosewheel) but possibly injury as well.

 

Which is why I said with the gear aligned head on. I realize that during pushback it would not be a good idea. (or if anyone turned the tiller)

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