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Home > Air Safety > Is the plane's safety compromised when an engine cannot start on the ground?
Is the plane's safety compromised when an engine cannot start on the ground?
Aviation - Air Safety
Sunday, 12 September 2010 03:54

Hi Captain Lim,

Once when I was about to board a 1-hour flight in Florida, the plane's take-off was delayed for a good hour to an hour and 15 minutes.

We kept asking the flight attendants and apparently they couldn't get one of the engines started without the help of some giant fan machine to "jump start" one of the engines by blowing air into it. The ground crew could not locate the machine and I saw the pissed off captain exit the plane to yell at some people.

They were finally able to locate this machine and get the engine started, but I can sense an air of uneasiness on the plane. I have never been more afraid to fly in my life because I was sure I was flying on a plane with a defective engine. I was seriously considering telling them to let me off so I can catch a later flight. Don't planes start the engines without external equipment?

Captain Lim, what is this machine and what is this process of starting the engine? Is this a normal occurrence or only for older planes with malfunctions? Was my safety compromised by being in this plane with an engine that cannot start itself?
 
Ken.
 
Hi Ken,
 
The machine is known as the external air cart that supplies powerful compressed air to start the engines of the plane.
 
Normally airplane engines are started by compressed air from the plane own power source known as the APU (auxiliary power unit). Airplane engines must be accelerated to a high rotational speed in order to provide sufficient air compression for self-sustaining operation. Just like anything else, the APU may at times be inoperative. For short flights, this may not be a critical item to prevent the aircraft from going on its journey. The alternative is get an external air cart to start the engines, continue with the flight and gets the APU rectified on the next available downtime.
 
Yes, this is fairly normal and it does not necessary occur on older planes only. Your safety is not compromised for there are legal guidelines when a plane can continue with or without a serviceable APU.
 
So is the plane safety compromised when an engine cannot start on the ground? No, when one engine is started by the external power cart initially, the other engine can be started on the ground or in the air by what is known as cross-bleed starting.
 
How a jet engine works

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What if both engines need to be restarted mid-flight but the APU is still inoperative?
Hi Captain Lim,

Thanks so much for the response! It has helped me understand the process more.

You mentioned that if one engine was started, you can use a cross-bleeding feature to start the other engine without the cart.

My question is this:

What if BOTH engines died mid-flight for some reason and they both have to be restarted but the APU is out? What would you do in this situation to get the engines started again?
Ken , 12 Sep, 2010
What if both engines need to be restarted mid-flight but the APU is still inoperative?
Yes, I forgot to mention that in the worst case scenario when both the engines are failed, it is still possible to start the engines by what is known as the "air start" or "windmilling start" procedures.

Hence a windmilling start will be used to relight the engines when the engine starter or compressed air from another engine (cross-bleed) is not available.

In this case, the compressors are being turned by the natural airflow. The compressed air is then delivered to the combustion chamber where the fuel and the ignition sparks are introduced. This would enable the engine to begin a stable relight provided the airspeed is between 280 to 300 knots.
Captain Lim , 12 Sep, 2010
Failure of Generator , Low-rated comment [Show]
technical staff
Hi captain Lim
I'm a appy at S.A.A.T.I have a Question about technical staff which i need to know before i get to the hangers.just hope u can help me.
Heres my question,why do aircraft use 115v a.c while the galley section use 110v.
john , 30 Jul, 2014
Retired
This put my mind at ease because this just happened in Las Vegas. I have flown for years in a 210 Cessna and my friend, the pilot, always reassured me that he wants to live as much as I do so relax, we will get there safe. I always think of his statement and I know the pilot will not take the plane up if there is a problem. Thanks for your input.
Pat hayes , 05 Jun, 2016

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