Battery switch in flight

[andreasxb]

Sooo I was in cruise and wanted to try out what happens if you switch the battery to off. I was thinking it would just disconnect the battery, disabling backup functions and charging. I figured out afterwards that I was wrong on the charging, that happens no matter what. Also it's not just backup, everything on the Switched Hot Battery Bus is then unpowered, if I read it right.

In the IXEG however, all power was lost as the generators were also kicked off their buses. I could turn the switch back on and reconnect the generators, but I lost alignment on the INS units (as they lost both AC and DC) and I lost pressurization (that could have been me misinterpreting things and making it worse myself, so maybe ignore this). This also caused a huge speed to be displayed in the MCP speed window until I adjusted it, as seen in: 

 

[Litjan]

Hi Andreas,

yes, unlike on the Airbus, a lot of stuff hinges on the battery (like the power to the generator breakers), and switching it OFF will leave you with nothing but the hot battery bus (and ground service, if there is a GPU plugged in and the switch is toggled - this is not modeled yet). Onlike Airbus, Boeing relies on their pilots to have a brain and not turn off the battery switch until they have a VERY good reason to do so and understand the consequences ;-)

The IRS units have DC backup, but not on the hot-battery bus, so they will die, too. Pressurization should be able to be regained, you need to get the cabin back into parameters first with the Standby or Manual mode, then you can re-engage automatic mode (switch to standy and back).

You can re-align the IRS in attitude mode, but the position will be lost - however the GPS will work, so that is not the end of the world.

The "huge speed" inthe MCP speed window is definitely a bug, some situation that you guys are getting yourself into that we haven´t tested for... I will try to recreate this myself and then we put some sort of stopgap to the maximum speed. I am a little wary of tinkering with that code too much, Tom and I want to really rip the guts out of VNAV and then sow everything back in neatly in a future update, and this will likely affect many of these quirky speed calculations...

Cheers, Jan

 

[judeb]

Sorry, can't stop laughing at your brain reference.

Sent from my Swift 2 Plus using Tapatalk

[andreasxb]

13 hours ago, Litjan said:

yes, unlike on the Airbus, a lot of stuff hinges on the battery (like the power to the generator breakers), and switching it OFF will leave you with nothing but the hot battery bus (and ground service, if there is a GPU plugged in and the switch is toggled - this is not modeled yet). Onlike Airbus, Boeing relies on their pilots to have a brain and not turn off the battery switch until they have a VERY good reason to do so and understand the consequences ;-)

Forget pilots doing stupid things, are you serious about one single device failure being able to take down all of a 737's systems without backup or redundancy? I find it hard to believe that such a death trap would be permitted to fly much less carry passengers.

I mean, I was able to divert to EDDF after I decided to treat this as an emergency rather than abort the flight, but after all I was able to just flip the battery switch back on which is not an option when it fails.

Anyway, using this schematic as a reference, the generator power control should be on the hot battery bus. According to my reading, turning battery off should mainly lose reverser control on the switched battery bus, whereas the battery bus would continue to be powered by TR3.

[Ben Russell]

2 hours ago, andreasxb said:

Forget pilots doing stupid things, are you serious about one single device failure being able to take down all of a 737's systems without backup or redundancy? I find it hard to believe that such a death trap would be permitted to fly much less carry passengers.

I mean, I was able to divert to EDDF after I decided to treat this as an emergency rather than abort the flight, but after all I was able to just flip the battery switch back on which is not an option when it fails.

Anyway, using this schematic as a reference, the generator power control should be on the hot battery bus. According to my reading, turning battery off should mainly lose reverser control on the switched battery bus, whereas the battery bus would continue to be powered by TR3.

How is this any different to just turning off the engines and pitching down hard?

Where do you draw the line?

[Litjan]

Hmm, I think if the battery switch breaks, it won´t be dangerous. Either it breaks on the ground, in that case you can´t even power up the aircraft. Or it breaks during flight, in that case you will notice when you try to shut down the aircraft for the night.

There could be one good reason for turning it off during the flight on purpose: If both generators fail and the APU does not start, you are down to 30 minutes of flight powered by the battery. If you are 1 hour away from the next airport (and it isn´t CAVOK all the way) you would face the descision to either ditch/force land now, or to switch of the battery. Now you can fly for as long as you want (use dead reckoning and the standby instruments) - then when you are close to your airport, turn everything back on, align IRS in ATT mode, fly an ILS approach.

I am fairly certain that switching off the battery will also disconnect the generators - you can´t see the dependency from the regular wiring diagrams, but I think it switches the exciter field of the generator breaker solenoids off.

Cheers, Jan