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Loss of thrust (both engines) on 737/320

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Loss of thrust (both engines) on 737/320

Old 22nd Apr 2023, 08:28
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Smile Loss of thrust (both engines) on 737/320

So, I was basically working on a project where I'm analysing some crucial decision making processes that pilots would undergo during a Non normal scenario.

One of the key ones, is of course, a Dual Engine Failure.

The question is, would you attempt multiple windmill relights, while being at a non-optimal speed (Above Green Dot in the case of a 320) or would you rather go for best glide speed (At or Near Green Dot), and try a Bleed Air start via APU.

A few important factors to consider (in my opinion):
1. Modern Engines are insanely reliable- Thus, for 2 simultaneous failures to occur, you almost certainly have a common issue (no fuel, contaminated fuel, failure of suction feed due to G-Force, severe icing, birdstrike)
2. Nearest Airfield- If anyways you are not gonna be able to land at an airfield at best glide (for eg. during ETOPS), then I would assume that you'd try your best to get the engines started.
3. Pressurisation- A higher FL (like FL400) would be quite problematic in terms of pressurisation, especially if you're gonna descend at Green Dot, since APU Bleed might not be enough



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Old 22nd Apr 2023, 09:07
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Whatever might be concluded in theory, calm thoughts remote from a real event, it will not be reflected in practice.

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Old 22nd Apr 2023, 09:17
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Originally Posted by safetypee
Whatever might be concluded in theory, calm thoughts remote from a real event, it will not be reflected in practice.
I completely agree with you. In the Hudson ditching, the switching on of the APU was an excellent choice (and an example of how good systems knowledge is incredibly important).

My only point here was, that with a Dual Eng. Failure @ Cruise, you would have a certain amount of time to make the decision to fly green dot or faster... with potentially severe consequences.
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Old 22nd Apr 2023, 09:34
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Originally Posted by Zar_1
So, I was basically working on a project where I'm analysing some crucial decision making processes that pilots would undergo during a Non normal scenario.

One of the key ones, is of course, a Dual Engine Failure.
These studies have already been done on the ground and are reflected in the checklists.

The basic philosophy of Boeing is that if it is a dual engine failure, the possibility of having a dual _catastrophic_ failure is extremely remote. So the initial reaction high altitude is always to go for a higher speed and a restart to get at least one engine running again (and it doesn't stop you from steering into a certain direction).It is only once you start to pass FL200-150 the APU becomes an option and you can have some kind of idea of what caused the dual engine failure and you can adapt your actions.

Some people will say: what if you are remote from an airfield? The fact you are remote is a pretty clear indication the engines have been working fine for a long time, so the source of the dual engine failure is "outside" and "local". Hence you need to clear the area as quickly as possible (in case of volcanic ash, a descent is the way to go), keep high speed, and continue to go for optimal speeds for restarts.

Last edited by BraceBrace; 22nd Apr 2023 at 09:48.
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