When something goes wrong while flying on the Boeing 737, we use the QRH (Quick Reference Handbook). We just have to find out the correct NNC (Non Normal Checklist) and then we just read it and execute it.
For some of these checklists, we have memory items, meaning we have to know by heart some actions.
I have listed 9 memory items:
- Aborted Engine Start
- Airspeed Unreliable
- APU Fire
- Cabin Altitude Warning / Emergency Descent
- Engine Overheat
- Engine Fire, Severe Damage or Separation
- Engine Limit or Surge or Stall
- Loss of Thrust On Both Engines
- Runaway Stabilizer
Engine Fire, Severe Damage or Separation
Autothrottle (if engaged) ...................................Disengage
Thrust lever
(affected engine).....................Confirm....................Close
Start lever
(affected engine).....................Confirm...................CUTOFF
Engine Fire switch
(affected engine).....................Confirm.....................Pull
To manually unlock the engine fire switch, press the override and pull
If the engine fire switch or ENG OVERHEAT light is illuminated:
Engine fire switch...........................Rotate to the stop and
hold for 1 second
If after 30 seconds the engine fire switch or ENG OVERHEAT light
stays illuminated:
Engine fire switch...............................Rotate to the
other stop and
hold for 1 second
Although we have 3 different problems with the engine, the checklist and memory items are the same here but a good diagnosis is vital to avoid complication.
First it is important to remember that there is no memory items for an engine failure. Why? Because you can still fly the airplane on one engine and there is no major threat associated. That’s why we first control the aircraft, retract the flaps, climb to a safe altitude and then do the non-normal checklist. If possible, try an in-flight engine start.
But for an engine fire, severe damage or separation, the aircraft is not safe and some actions are necessary rapidly to secure the engine and the aircraft it-self. As soon as we reach 400ft AGL, we complete the memory items.
Engine Fire
An engine fire is obvious and easy to detect. You get the fire warning bell associated with the engine fire light in front of you and finally the engine fire switch for the affected engine illuminates. On the newest versions of the 737-800 and 737 MAX, the engine start lever illuminates red as well. Once you have identified the problem, it is best to cancel the warning, it will shut the annoying bell.
The video below is nicely done and explains very well the different steps to control an engine fire:
Engine Severe Damage
Signs of an engine severe damage:
- Sudden loss of thrust
- A loud bang or multiple loud bangs
- No rotation of N1 and N2 very low
- Loss of engine indications
- High vibration levels either indicated or physically felt/heard but it’s possible to have no vibrations as well (interesting to know that engine high vibration starts at 4 units in the QRH)
- Multiple system failures (engine driven generator, engine driven hydraulic pump…)
The engine is severely damaged, you cannot try to restart it and you will either return to your departure airport or divert knowing that in this configuration you are CAT I limited.
Note: When N2 drops below 50%, the Engine Failure alert appears on the EGT gauge.
Engine Separation
An engine separation basically means that you physically lost your engine. This can of situation is really rare but it’s also easy to diagnose as you lose all your engine indications (either nothing or 0 indicated).
The handling of the aircraft will be more difficult. On the side your engine has separated, there is no drag anymore.
It is important to complete the memory items and to pull the engine fire switch because this closes both the engine fuel shutoff valve and the spar fuel shutoff valve and prevent from a massive overboard fuel leak.
Here is also an old but super interesting video describing all turbofan engine malfunctions:
