Starting Engine without APU

Disclaimer: 

▪︎This content is Not an official document and does not represent the views of Airbus or any other aviation authority.

▪︎The information provided may be incorrect or misinterpreted and should not be relied upon for decision-making. 

▪︎Always refer to official documents and consult with a qualified aviation professional before making any decisions based on the information provided in this blog post.

▪︎The information provided in this blog post is based on personal study and review.

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GPU(External Power), ASU(Air starter Unit), ACU (Air Condition Unit)

 

When dealing with a malfunctioning APU, the aircraft should initiate engine start using an Air Starter Unit. 

 

 

 

External power (GPU) is necessary to maintain the aircraft's electrical power until the first engine is successfully started. Additionally, the Air Starter Unit is essential for supplying bleed pressure to initiate the engine start.

when you have MEL with inoperative APU, the aircraft should start the engine with Air starter unit.

 

and in case of hot weather, Air condition Unit should connected for the passenger's comfort. 

 

Which Engine to start first? 

According to the FCOM "ENGINE START WITH AN AIR START UNIT" procedure, 

either Engine 2 or Engine 1 can be started first. 

In real life, the sequence may depend on operational considerations such as the location of the external power source and airport restrictions that permit starting the engine with the air starter unit while connected to a bridge electric source.

Since the GPU and Air Starter Unit need to be connected simultaneously, the physical placement of these ground equipment items at specific airports varies.

ENGINE START WITH AN AIR START UNIT (part of procedure)

 

 

And if Engine 1 were to be started first, it is necessary to check ACCU pressure to prevent the PTU from running, as parking brake pressure is linked to the yellow hydraulic system.

 

 

Location of deboarding bridge and GPU.  ACU(Air condition Unit) 

Whether there is a boarding bridge or a step car to disembark the passengers, it is usually the left side of the aircraft where passengers disembark. For this reason, when the aircraft is parking at the parking spot, they position the GPU on the right side of the aircraft. So, when they need to start the first engine before pushback

(the aircraft needs to start at least one engine before pushback),

it would be easier to locate the ASU on the left side since the right side is already occupied by the GPU.

 

the pilot needs to confirm which engine to start first with ground staff but it is usually the left engine(#1 engine) to start with ASU at the parking spot. 

 

And this starting process without APU takes longer than starting with APU. 

Ground staff need to complete cargo loading, remove the Air Conditioning Unit, 

and bring the ASU to connect to the left engine (#1 engine).

To expedite this process, especially in hot weather when the ACU is connected to the aircraft,

In my experiences. it usually depended on how quickly they can remove the Air Conditioning Unit. 

If it is possible to disconnect the Air Conditioning Unit before finishing cargo loading or passenger boarding, it can expedite the process of starting the first engine at the parking spot and reduce the time of the flight delay.

 

 

 

CROSSBLEED ENGINE START

After the first engine is started and GPU and ASU are removed, it is time to request pushback. 

Even though it would be possible to start the second engine using ASU at the parking spot, now that the engine is running on the left side (#1), the ground staff do not have enough space to locate the ASU with the running engine on the left side. 

Although it is possible to position the ASU and GPU on the same side, this time with one engine running, it might be dangerous for them to start the remaining engine with all these equipment and the other engine running. 

Additionally, airports usually do not permit starting both engines at the parking spot, so we need to push back the aircraft and initiate the remaining engine start using the crossbleed engine start procedure.

 

 

 

 

CONSIDER MEL. ( ENGINE BLEED MEL and APU INOP )

And there is one MEL which impacts the starting sequence of the engine without APU: the Engine Bleed System.

MEL : ENGINE BLEED SYSTEM

 

If the aircraft has a simultaneous MEL with APU and engine bleed, the operating side of the engine bleed needs to be started first to enable cross-engine bleed start with the inoperative side.

CROSSBLEED ENGINE START procedure

For example, if there is an Engine 1 bleed system malfunction, Engine 2 needs to be started first at the gate.

If Engine 1 is started first and we were to start Engine 2 with a crossbleed start after pushback, since the Engine 1 bleed system is malfunctioning, there is no supplying engine bleed available for Engine 1.

So if that happens, they would need to either bring ASU again after pushback or return to the parking spot, shut down Engine 1, and start Engine 2 again with ASU unless they can start the remaining engine with ASU with the other engine running.