I've had this a/craft for years and have always followed the same engine start procedure. Start the APU and then open the APU bleed valve. Then, still on the overhead, switch the isolation valve from "auto" to "on" and the manual valve from "closed" to "open". Then turn the appropriate start switch to ground and switch the fuel lever when N2 is approx 20.The other day I realised that for some reason I had missed out two of these steps, switching the isolation valve to "on" (it was left in "auto") and switching the manual valve to "open" but the engines started the same. Next day, to check, I did this deliberately and yes the engines started without these two switching actions.Is this accurate or a fault in the design of this model?Iain Smith

I'm not type rated but it seems logical that the automation would leave the isolation valve in OPEN (I assume this is what you mean by "on") unless there was a condition that would call for a CLOSED valve. Therefore, AUTO = OPEN in the engine start scenario. Some aircraft turn the packs OFF for start or takeoff but I don't recall the proper operation of packs in the 737, but this is not your question. I'd venture the sim is correct.

I've had this a/craft for years and have always followed the same engine start procedure. Start the APU and then open the APU bleed valve. Then, still on the overhead, switch the isolation valve from "auto" to "on" and the manual valve from "closed" to "open". Then turn the appropriate start switch to ground and switch the fuel lever when N2 is approx 20.The other day I realised that for some reason I had missed out two of these steps, switching the isolation valve to "on" (it was left in "auto") and switching the manual valve to "open" but the engines started the same. Next day, to check, I did this deliberately and yes the engines started without these two switching actions.Is this accurate or a fault in the design of this model?Iain Smith

Iain,I'm not sure I entirely understand your post, but I'll take a stab at it.In regards to the "manual valve," I'm guessing you're talking about the manual pressurization outflow valve control. That switch has no effect on starting. Usually, the pressurization mode selector is left in auto, unless you close it to prevent aft lav water lines from freezing (cold weather ground operations). The isolation valve in either auto or open will allow the engines to start (if the packs are off). On the ground, the usual situation is that the APU is providing air to both packs and both packs are in auto. With the isolation valve in open, the right pack can get air from the APU. After the engines are started, the APU bleed is off and the isolation valve is in auto.The only thing leaving the isolation valve in auto on the ground would have done is you wouldn't have gotten air to the right pack for air conditioning before the start. When you turned off the packs to start, the auto mode opened the isolation valve so you could start the #2 engine.Clear as mud?

.../...Then turn the appropriate start switch to ground and switch the fuel lever when N2 is approx 20.Iain Smith

Hi Iain,For information, the real procedure says that N2 should indeed be at the minimum 20% BUT that the desired condition for fuel cut-in is either N2 >= 25% or Max Motoring (ie increasing by less than 1% in 5 seconds).To me, this means that a value above 20% but inferior to 25% is acceptable only if Max Motoring has been reached. The procedure also states that "advancing start lever prematurely can cause a Hot Start".Rgds,Bruno

Hi guy's. I noticed that also you can start engine 2 from bleed air from engine 1 without increasing n1%. on the real aircraft and in the procedures it states that a minim of 40% n1 sould be reach to turn over engine 2 to get 20% or 30 psi duct pressure. In the PMDG 737 i don't need to increase engine1, engine 2 starts straight away. The tin mouse 737-200 models this well This taken out of 737-800 procedure.......................................................................................................................................................Engine Cross Bleed StartPrior to using this procedure ensure area to rear is clearEngine BLEED air switchs..................................ONAPU BLEED air switch.......................................OFFPACK switchs .................................................OFFISSOLATION VALVE switch...............................AUTO Ensures bleed air suply for engine startEngine thrust lever (opperating engine).... Advance thrust lever until bleed duct preesure indicates 30 PSIUse normal start procudure with cross bleed startAfter starter cut out adjust thrust on both engines as required...................................................................................................................................................................Thats why this plane hit the tug on the tarmac http://www.aaib.gov.uk/cms_resources.cfm?f...DLR%2012-09.pdf

Hi guy's. I noticed that also you can start engine 2 from bleed air from engine 1 without increasing n1%. on the real aircraft and in the procedures it states that a minim of 40% n1 sould be reach to turn over engine 2 to get 20% or 30 psi duct pressure. In the PMDG 737 i don't need to increase engine1, engine 2 starts straight away. The tin mouse 737-200 models this well This taken out of 737-800 procedure.......................................................................................................................................................Engine Cross Bleed StartPrior to using this procedure ensure area to rear is clearEngine BLEED air switchs..................................ONAPU BLEED air switch.......................................OFFPACK switchs .................................................OFFISSOLATION VALVE switch...............................AUTO Ensures bleed air suply for engine startEngine thrust lever (opperating engine).... Advance thrust lever until bleed duct preesure indicates 30 PSIUse normal start procudure with cross bleed startAfter starter cut out adjust thrust on both engines as required...................................................................................................................................................................Thats why this plane hit the tug on the tarmac http://www.aaib.gov.uk/cms_resources.cfm?f...DLR%2012-09.pdf

What is a "hot start?" Manual warns against but doesn't explain it.Fidel Lopez

What is a "hot start?" Manual warns against but doesn't explain it.Fidel Lopez

During a turbine engine start-up, it is possible for the temperatures inside the combustion section to get hot enough to cause internal damage to the engine. The engine manufacturer has determined a specific "do not exceed" temperature for each engine, and pilots monitor the IT gauges carefully during start-up to insure the engine does not exceed that limit. Some aircraft have manual 'trim' controls that pilots can use to reduce the amount of fuel flowing into the engine, while others have auto-trim, but either way, if the internal temperature of the engine goes over the established limit for a certain time period, you have a hot start. Hot starts will frequently require the engine to be removed from service and a complete tear-down and internal inspection of the engine will be performed to determine if there was damage, and if it can be repaired.

During a turbine engine start-up, it is possible for the temperatures inside the combustion section to get hot enough to cause internal damage to the engine. The engine manufacturer has determined a specific "do not exceed" temperature for each engine, and pilots monitor the IT gauges carefully during start-up to insure the engine does not exceed that limit. Some aircraft have manual 'trim' controls that pilots can use to reduce the amount of fuel flowing into the engine, while others have auto-trim, but either way, if the internal temperature of the engine goes over the established limit for a certain time period, you have a hot start. Hot starts will frequently require the engine to be removed from service and a complete tear-down and internal inspection of the engine will be performed to determine if there was damage, and if it can be repaired.

Hi ?A Engine Hot/Hung start is a engine start when the EGT exceeds the safe limits, Hot starts are caused by to much fuel is entering the combustion champer or the RPM of the turbine is insufficent. When this happen cutoff the fuel supply and continue with max motoring the engine for 5 minutes to cool down the core of the engine and blow out the remaining fuel than shutdown the engine. After approx 10 to 15 minutes retry to start the engine again for 1 more time. Most of the time the engine start normally. When the problem appears again hand over the airplane to maintenance for inspection. I am Ground engineer on the 737 Next Generation for 10 years now. I Have seen several hot starts. Only ones I had to replace the engine due to high turbine damage. Greetings Mark.