Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

AW139 Battery start procedure

Rotorheads A haven for helicopter professionals to discuss the things that affect them

AW139 Battery start procedure

Old 29th Nov 2017, 05:56
  #1 (permalink)  
Thread Starter
 
Join Date: Mar 2017
Location: JPN
Posts: 17
AW139 Battery start procedure

For battery start procedure, there is a NOTE as follows;


If engine N°2 is to be started first, set BUS TIE switch to ON and confirm MAIN BUS 2 voltage is not below 23V.


I thought ENG 2 Starter/Generator was powered by DC MAIN BUS 2, so we got to set BUS TIE SW to ON to start No.2 ENG first, but it is described in RFM 3-51 that ENG 2 IGNITER & START is powered by DC ESS BUS 2.


I wonder if we can start No.2 ENG first with BUS TIE SW in AUTO position in battery start.
twinbird is offline  
Old 29th Nov 2017, 06:13
  #2 (permalink)  
 
Join Date: Sep 2014
Location: On land
Posts: 120
From the AW tech notes

ELECTRICAL POWER – MAJOR COMPONENTS
STARTER-GENERATOR
Two 9-kW DC starter-generators are used to start the relevant engine and, when the engine is running, to produce DC power.
The starter-generator no. 1 is connected to the MAIN BUS 1; the starter- generator no. 2 is connected to the MAIN BUS 2.
If the bus tie is left in auto in the situation you describe, the no2 starter gen will not be powered.
Nescafe is online now  
Old 29th Nov 2017, 06:20
  #3 (permalink)  
 
Join Date: Sep 2014
Location: On land
Posts: 120
BATTERY STARTING
The following diagrams represent the sequence of actions for a normal battery starting of the engines (steps 1 to 8 on the simplified schematic diagram). In this example engine no. 2 is started first.
Refer to AW139-RFM-4D – Section 2 for Normal Procedures.
STEP 1
Helicopter is parked and ready for flight. All switches are in the safe position.
STEPS 2 TO 3
When BATTERY MASTER switch is set to ON, Main and Aux Batteries are connected to ESS BUS 1 and ESS BUS 2 thus providing power to the rotorcraft essential loads.
The BATTERY MASTER switch at ON also enables the BATTERY MAIN and the BATTERY AUX switches.
When BATTERY MAIN switch is set to ON, the Main Battery is connected to MAIN BUS 1 (Main Battery contactor K3 closes) which is then also powered. When BATTERY AUX switch is set to ON, the Auxiliary Battery is connected to MAIN BUS 2 (Aux Battery contactor K4 closes), but MAIN BUS 2 is notpowered because of the reverse biased diode (CR5) which only permits recharging of the Auxiliary battery from MAIN BUS 2.
When GEN 1 and GEN 2 switches are set to ON they give an input to the relevant GCU so that the GCU will put the relevant generator on-line as soon as conditions permit.
23 VOLT CHECK
Before attempting starting the engine on batteries, the pilot has to check that the involved MAIN BUS voltage is not less than 23 V.
STEP 4
As in this example the engine no 2 is started first, the BUS TIE switch must be set to ON to power MAIN BUS 2.
BUS TIE Contactor closes thus connecting MAIN BUS 1 and MAIN BUS 2.
Nescafe is online now  
Old 29th Nov 2017, 15:21
  #4 (permalink)  
 
Join Date: Sep 2004
Location: daworld
Posts: 608
twinbird, which battery is used for starting the engines and where is it located?

Answer: Main Battery and it is on the #1 side. So you need Bus Tie ON as you are cross feeding electrical power to start #2 on battery. If you set Bus Tie to AUTO and the voltage drops below a prescribed value, the Bus Tie will disconnect and the starter will disengage.

Battery start is always quicker on #1 engine. Less diodes to go through, so less voltage drop.
noooby is offline  
Old 29th Nov 2017, 23:47
  #5 (permalink)  
 
Join Date: Sep 2011
Location: USA
Age: 50
Posts: 222
https://www.youtube.com/watch?v=HNjCL651-dU



Explanation at 1.00
Sir Korsky is offline  
Old 30th Nov 2017, 04:17
  #6 (permalink)  
Thread Starter
 
Join Date: Mar 2017
Location: JPN
Posts: 17
Thank you very much for all the replies. I understand the system overview,


but how should I get the fact that ENG 2 IGNITER & START is powered by DC ESS BUS 2.


I'm confused...
twinbird is offline  
Old 30th Nov 2017, 06:18
  #7 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 2,483
Equally confusing is the mix of switch directions.

In the S76, everything ON is forward.

In this one, electrical switches ON are rearward, but fuel switches, pumps etc are Forward.

A potential for finger trouble - everything should be consistent, either all forward for ON, or all backward, it is dangerous to have a mix.
Ascend Charlie is offline  
Old 30th Nov 2017, 06:45
  #8 (permalink)  
 
Join Date: Sep 2014
Location: On land
Posts: 120
In this one, electrical switches ON are rearward
Not so. Everything goes forwards to go on.

Edit: if you are referring to the YouTube clip, the switches you see are on the overhead panel, they are moved forwards to the on position.
Nescafe is online now  
Old 30th Nov 2017, 07:19
  #9 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 2,483
AHA!!

Thank you. Forward is ON, all good. The 76 had almost everything on the lower console.
Ascend Charlie is offline  
Old 30th Nov 2017, 07:35
  #10 (permalink)  
 
Join Date: Aug 2001
Location: Cornwall
Age: 71
Posts: 1,305
Starting No 2 first.....

..... why would you. Placing the Bus Tie Switch ON will load up the battery with the services on the Main 2 BB - not so smart if you are short of battery volts.

It is possible to start an engine with less than the required 23v but this is not recommended by the engine manufacturer because the resulting engine acceleration is too slow. This results in a low cooling air mass flow through the turbine area internals. This can lead to extreme heat in areas where the subsequent excessive metal expansion causes blade-rubbing on the inside of the turbine case. At the next internal inspection, the engine would be pulled for an overhaul.

A 'one-off' such start in extremis would probably be OK but those that have done it habitually have paid the price.

G.
Geoffersincornwall is offline  
Old 30th Nov 2017, 19:36
  #11 (permalink)  
 
Join Date: Feb 2005
Location: On the green bit near the blue wobbly stuff
Posts: 599
TWINBIRD,

You are quite right, it is confusing. Both QRH and RFM say that the starter gens are on DC essential, and they are appear to be in the DC essential area on the overhead c/b panel. So why do all the training manual circuit diagrams show them off the main buses?
I have been trying for a couple of days to bump into one of the groundschool experts and ask them over a coffee. If I manage to pin them down and get an answer, I will post it on here.
Non-PC Plod is offline  
Old 30th Nov 2017, 23:01
  #12 (permalink)  
 
Join Date: Dec 2007
Location: the land of redemption
Age: 48
Posts: 247
There is one way only to start up engine n°1 (this is the less battery consuming engine) without GPU with main battery with less than 23V and/or residual ITT > 280°C and without having vented (dry motored) the engine before shut down.

The procedure is out of the manuals, its name is "semi-automatic procedure".

Sure lot of gentlemen are aware of this.
maeroda is offline  
Old 1st Dec 2017, 01:36
  #13 (permalink)  
 
Join Date: Sep 2004
Location: daworld
Posts: 608
Lots of things aren't in the manuals (unfortunately). Like how to recharge the batteries from GPU. Very simple, but not in the manual!
noooby is offline  
Old 1st Dec 2017, 03:29
  #14 (permalink)  
 
Join Date: Sep 2011
Location: USA
Age: 50
Posts: 222
The bus tie closes when manually switched to the on position. It will close in Auto mode when external power is connected or when one gen is failed. I was told there is a remote chance the auto mode could open the bus during the start sequence resulting in an inadvertent hot start on the #2 engine.
Sir Korsky is offline  
Old 1st Dec 2017, 08:54
  #15 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,485
Like how to recharge the batteries from GPU. Very simple, but not in the manual!
out of interest, what are peoples thoughts about this?

There have been concerns on other types that allowing a rapid charging with the GPU
- following a low batt voltage situation for example - could create conditions for thermal runaway in the battery.
crab@SAAvn.co.uk is offline  
Old 1st Dec 2017, 09:57
  #16 (permalink)  
 
Join Date: Sep 2014
Location: On land
Posts: 120
If you have gpu available, wouldn’t the safest option be to use it to provide start power, then let the battery recharge in the manner intended?
Nescafe is online now  
Old 1st Dec 2017, 13:07
  #17 (permalink)  
Thread Starter
 
Join Date: Mar 2017
Location: JPN
Posts: 17
Originally Posted by Non-PC Plod View Post
TWINBIRD,

You are quite right, it is confusing. Both QRH and RFM say that the starter gens are on DC essential, and they are appear to be in the DC essential area on the overhead c/b panel. So why do all the training manual circuit diagrams show them off the main buses?
I have been trying for a couple of days to bump into one of the groundschool experts and ask them over a coffee. If I manage to pin them down and get an answer, I will post it on here.
Thank you very much Non-PC Plod!
I look forward to the answer.
twinbird is offline  
Old 1st Dec 2017, 13:08
  #18 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 7,485
Yes, but what happens if you go out to the aircraft and discover someone has left a direct service on and the battery is lower than min for start? If you don't have the time to change the battery, do you start it on GPU and then let the aircraft or GPU push charge into it?
crab@SAAvn.co.uk is offline  
Old 1st Dec 2017, 13:16
  #19 (permalink)  
Thread Starter
 
Join Date: Mar 2017
Location: JPN
Posts: 17
Originally Posted by maeroda View Post
There is one way only to start up engine n°1 (this is the less battery consuming engine) without GPU with main battery with less than 23V and/or residual ITT > 280°C and without having vented (dry motored) the engine before shut down.

The procedure is out of the manuals, its name is "semi-automatic procedure".

Sure lot of gentlemen are aware of this.
I had a few times to start engine with less than 23V battery. I was lucky that I only had several unfamiliar CAS messages, but didn't have DUs black out. I heard DUs black out happened in the situation.


Could you let me know the way called "semi-automatic procedure".
twinbird is offline  
Old 1st Dec 2017, 15:05
  #20 (permalink)  
 
Join Date: Mar 2002
Location: West of zero
Posts: 237
I thought ENG 2 Starter/Generator was powered by DC MAIN BUS 2, so we got to set BUS TIE SW to ON to start No.2 ENG first
This is correct.
but it is described in RFM 3-51 that ENG 2 IGNITER & START is powered by DC ESS BUS 2
This is NOT correct. There is no circuit breaker between the starter/generator and the respective main bus (in this case, main bus 2), but a "contactor"; in essence, a relay. This relay is powered by the respective essential bus, not the starter itself.
Battery start is always quicker on #1 engine. Less diodes to go through, so less voltage drop.
Bingo. Only time I'll agree to start #2 off internal battery is with both good voltage and cold engine. We tend to park with left side upwind so this is "almost never".
how to recharge the batteries from GPU. Very simple, but not in the manual!
I like that too! That way it's the engineers who'll be responsible for choosing that short-cut and the resulting hot start or worse if some battery cells happen to be damaged rather than the battery depleted. The level of system knowledge displayed here supports not letting pilots make these calls.
It will close in Auto mode when external power is connected or when one gen is failed.
At the time of starting the first engine NEITHER generator is working so the bus tie will be open => no power on main bus 2 => no power to starter/generator 2 even if the starter/generator "contactor" (see above) is closed.
out of interest, what are peoples thoughts about this?

There have been concerns on other types that allowing a rapid charging with the GPU
- following a low batt voltage situation for example - could create conditions for thermal runaway in the battery.
If you have gpu available, wouldn’t the safest option be to use it to provide start power, then let the battery recharge in the manner intended?
Would you rather have a thermal runaway in an empty aircraft sitting on the ramp, or in an aircraft with both engines running, and you being strapped inside it? Also, the GPUs I've used had slightly lower voltage (and therefore, lower charging current) than the generators gave after engine start, therefore IMO a lower chance of thermal runaway.
Yes, but what happens if you go out to the aircraft and discover someone has left a direct service on and the battery is lower than min for start?
This is indeed by far the most prevalent cause of low battery voltage on start-up, far more common than damaged battery cells or wiring/circuit faults, and is why recharging from the GPU is so popular.
If you don't have the time to change the battery, do you start it on GPU and then let the aircraft or GPU push charge into it?
How important is it to take off on that flight right now? Life or death type important? The procedure you propose definitely comes with an increased risk of problems that will preclude the flight from taking place at all, but maybe taking that chance is warranted under the circumstances? I only fly simple O&G offshore revenue flights and would rightly be censured for taking this option even if I were to get away with it.
I was lucky that I only had several unfamiliar CAS messages, but didn't have DUs black out. I heard DUs black out happened in the situation.
Not only that, the EECs (during engine start) and GCUs are also powered off the essential buses; would you even be able to abort the ongoing start when your only source of electrical power flakes out?
Could you let me know the way called "semi-automatic procedure"
I think it's in the RFM under "MANUAL ON GROUND START PROCEDURE". I would NOT recommend this for low battery voltage - if the screens blank out, how can you tell if the start is going hot? If you then abort the start because the blank screens, how do you know if you have pooled fuel inside the engine case still burning? Unless you see flames coming out of the exhaust once you get out, in which case what'll you do now, with really, conclusively, no battery power to speak of?
Buitenzorg is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.