737 800 fan blades and icy tail.
 

Hello all,

I see lots of pilots routinely turning fan blades on the walk around, is there any sense or reasoning for this?

Also what's the reason we get that little bit of ice forming on the vertical stab base after a long cold cruise?

Many thanks

Interesting questions, especially considering some of your other posts...e. g. 737 bleed config for G/A, TRE/TRI requirements, etc etc...

Turning fan blades is easy and quick and satisfying that no odd clicks are heard as well as adjusting the reflected light on the blade leading edges to see if abnormal FOD damage is present. It also helps one peek behind the fan deeper into the engine for anything amiss.

Not just on 73s but any high bypass engine:
To make sure the N1 spool is free to move and there is not a puddle of ice locking it, (first flight of the day), or some FOD.

A spinning spool allows you to see the stator vanes and the compressor intake behind the fan more easily.

Ditto to see the vanes in front of the turbine at the rear.

Ditto to see the condition of the rubbing seal strip round the edge of the fan.

The fin will have been cold soaked during the cruise and if the aircraft desends through moisture, ice may form. The base of the fin area might be aerodynamically 'quiet', so perhaps not enough airflow to disperse any ice, or more likely: the ice may form on the ground during the taxi in to the gate. A similar thing sometimes happens to the landing gear and the lower surface of the wing, under the the fuel tanks.

To add to all of that how else would you know about fan blade icing on the rear of the blade if you didn't touch it...?

In cold climates you may have a significant amount of ice on the fan blades if the engine covers weren't put on over night. Even on routine turnarounds you can find a smaller amount of ice accretion on the fan blades that built up during approach/taxi in.

So to avoid anymore unhelpful and sarcastic comments I shall add to my initial question.

I have been flying (and training) on the 800 for a few years now and have been taught to rotate the fan on every walk around by a few trainers for some of the reasons stated above. I was however told not to put my hands anywhere near the fan in recent times by a very experienced LTC, TRE and senior examiner. This confused me somewhat and caused me to seek clarification and learn something perhaps which might benefit my understanding.

I do check for ice on the fan blades in icing conditions but I don't turn the fan to do so.

I hope now you can understand the relavence of my questions.

What reason did he give you this experienced chap?
I have come across lots of techniques, opinions, pet peeves of various trainers. I listen, let it pass through the BS filter, either discard it or try to remember.

I have my own things, such as not walking in to the wheel well. Don't like the idea of walking into a gas chamber of Skydrol fumes (or worse, a jet). We've had an incapacitation as a result of it. I know what the book says, but no thanks. I can spot a leak by seeing wet ground underneath instead.

Just that he didn't think it was safe or necessary to check and that leaning on the acoustic lining regularly would cause problems.

Why would you need to 'lean on the acoustic lining'

It's not like you have to reach very far ?

Is your senior trainer very overweight? Too many trainers have their own "individual SOP's" that aren't based on anything factual! As mentioned above, apply your bull**** filter.

Rotating the fan provides the following assurances:

1. The fan assembly actually moves.
2. A confirmation of the absence of an unacceptable amount of ice.
3. You can see the inside of the bypass duct to confirm there is no debris or birds etc.
4. That all the compressor inlet and guide vanes are free from obvious damage and no obvious ingestion has taken place.
5. As the blades pass, they all look equal (ish) and there are no obvious buckles or dings.

That little area of ice at the base of the stab is were there is a big metal spar right under the skin where the fin attached to the fuselage. This coldsoaks in the cruise but has enough mass that unlike the skin and other lighter components in the tail structure it does not always warm above freezing up during the descent and so frost condenses on it on the ground.
You'll sometimes see similar effects elsewhere on the airframe (usually on the wing) where heavier structure lies close under the skin.

And if you cannot reach it? (e.g. 757/767)

@ testpanel, OK I could have phrased that better - I meant that I was not talking specifically about 737s, about which I know very little. How do you check the fan on 757/767 then ?

We were once told about an engineer who was working on a fan engine, removing the P1 probe. A part of the probe assembly fell back down the mounting hole and he put his finger in to try to retreive it, upon which the fan, (which was rotating due to the wind), cut his finger clean off !!

Perhaps this is what you were being warned about, but there is no such danger from gently grasping and turning a fan blade from the front - (just don't get your skin jammed between the tip of a blade and the abradable seal).

If, due to the wind the fan is turning any faster than very slow, don't touch it at all - there can be a lot of energy in a rotating spool and you could damage your hand.

As for damaging the acoustic lining, I don't know about Boeing, but on Airbus you would have to do something extreme to even make a mark. What the hell was your instructor doing?

In my experience, walkarounds are notoriously badly taught - if they are even taught at all. (In all my Airbus flying I have never been shown what to do by anybody), but your FCOM should have detailed instructions about what to do and look for.

He was right. My sciatica is a nightmare.

Yes, 5 by 5 now, thanks a bunch. Just to clarify: you're an instructor yourself (for a few years) but another instructor (just one) tells you something with (presumably) no backing other than his own opinion, and you're suddenly all confused and discombobulated? This guy really tell you to not go "anywhere near the fan"? I have a sense (hope?) you're putting us on.

Not that there's anything wrong with that...

Is it wrong to question what you know occasionally? Many times now I have questioned what I know, come on here for support and learned something new which has changed my understanding. Maybe I shouldn't bother.

A few years back I was on a Delta flight from LAX to ATL on an old L-1011. And just as the flight was passing east over the CA/AZ border, the center engine experienced a compressor failure that caused the entire aircraft to shake violently. We dropped altitude and returned to make a safe emergency landing at LAX. So everything worked out OK.

The question I have is how could a pilot perform a pre-flight check of an engine that is located like the center engine of an L-1011 or an MD-11?

They didn't........