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Eric_Parker

MD11 Nav lights

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I realize this may not be a big deal but the nav lights do not operate on only battery power. Since I haven't been able to find a wiring diagram, only schematics, I don't know how accurate this is. This would be the first airplane I have encountered that would be wired this way in my 50 years of aviation experience although I could be wrong. Yes, the nav lights will come on but only with external or APU power. Since FAA procedures specify nav lights on when an aircraft is powered up and the beacon light to be on when the engines are running, I don't understand why the airplane would be wired this way.

 

Eric Parker

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Because there is no need to turn on those light when only on Bat ;)

 

Modern aircraft has lot & lot of items running (computers, cooling stuff,...)  consuming an enormous quantity of electricity....

There is a average 15 minutes battery time on those big birds and if you add light, your drop down the battery time... that's useless...

You can't start without APU or GPU / start units you turn light on after GPU or APU is start up & then there is no more battery issue to come

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As I stated, FAA requirements specify Nav lights must be on when there is activity on the aircraft. That means if someone is in the aircraft.

 

There are many occasions when the APU or External power would not be used immediately. Having flown in air carrier aircraft I know this is the case. Have you ever been in the cockpit or worked on a real airplane?

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As I stated, FAA requirements specify Nav lights must be on when there is activity on the aircraft. That means if someone is in the aircraft.

 

There are many occasions when the APU or External power would not be used immediately. Having flown in air carrier aircraft I know this is the case. Have you ever been in the cockpit or worked on a real airplane?

FAR 91.209 only mandates that position (nav) lights be illuminated between sunset and sunrise, and then only when the aircraft is "operated" i.e. when the aircraft is in motion - either on the surface or in flight.

 

"Nav lights on" when the aircraft is occupied and powered on the ramp (day or night) is a recommended best practice by the FAA, but it is not regulatory. It is, however, a requirement of many, (if not most) airline SOPs.

 

There are MANY large commercial aircraft whose nav lights will not illuminate on battery power only - especially those with AC electrical systems that use TRUs (transformer rectifier units) to produce primary DC power.

 

No large aircraft will be operated using battery power only for more than a couple of minutes before applying external power or starting the APU (if so equipped) Typically only long enough to verify the battery voltage is at or above minimum, to verify that flap spoiler and gear handles agree with the actual positions of the control surfaces, and to perform an APU fire detection system test (if the APU is going to be used).

 

Some smaller biz jets and turboprops have no APU, and can perform an engine start using the battery only - but the operators of such aircraft will almost always choose to avail themselves of an external power cart assist for engine start whenever possible. Such aircraft typically are wired so that the nav lights will run off battery power, as are virtually all piston-powered GA aircraft.

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