737NG moderate rain

[framer]

Hi folks, Vol 1 says this;

If moderate to heavy rain, hail or sleet is encountered:
ENGINE START switches ....................................................... CONT
Autothrottle ............................................................ ............ Disengage
Thrust Levers ............................................................ ... Adjust Slowly
If thrust changes are necessary, move the thrust levers slowly.
Avoid changing thrust lever direction until engines have
stabilised at a selected setting. Maintain an increased minimum
thrust setting.
IAS/MACH .......................................................... Use a slower speed
Using a slower speed improves engine tolerance to heavy
precipitation intake.

Consider starting the APU (if available).

My questions to you are,
"How often do you see this proceedure being followed in moderate to heavy rain?"
and,
" Can anyone recall an instance of a CFM56 flaming out due water ingestion?"

Cheers, Framer

[HPbleed]

Several instances... please feel free to use google.

TACA Flight 110 - Wikipedia, the free encyclopedia

Im an Airbus guy but use the ignition fairly regularly in winter if there is yellow on radar, heavy rain or any standing water. It's free -and the only downside is a reduction in the ignition system lifespan

[framer]

From the wiki article,

The investigation concluded that the engines had failed "as a result of an inflight encounter with an area of very heavy rain and hail. A contributing cause of the incident was the inadequate design of the engines and that the FAA's water ingestion certification standards did not reflect the waterfall rates that can be expected in moderate or higher intensity thunderstorms."[2]

Thanks HP Bleed, They actually selected ignition on prior to entering by the sounds of it. It also seems that it was pretty severe TS with hail and probably heavy rain.
Any more examples anyone?

please feel free to use google.

Thanks Captain Bleed

[Don Gato]

I would definetly turn the A/T OFF. I've seen the throttles go to idle in level flight while on heavy rain and turbulence (probably due to sudden overspeed due to a gust). Reaction time while manually moving the throttles forward was unusually slow. Not something I would like to see again.

[lomapaseo]

Any more examples anyone?

I believe there was one in Greece before TACA.

Of course we don't need any more after learning our lesson in the TACA investigation.

Lots of changes have been made in the engines since then.

The awakening was to learn that low fan speed and high aircraft speed cause the water to not get centrifuged out the fan ducts (away from the burner). Of course the mass of hail in the mix also goes right through the fan and into the core like a miniture golf course golf ball through a windmill.

Keep the aircraft speed down (it's gusty as hell anyway) and the fan rpm up a tad. Meanwhile the engine guys can put in spinners and splitters behind the fan like an olympic ski jump to coax the stuff to deflect out through the fan duct.

lots of other selective things can be done as well depending on the installation and the intended use (S-ducts, bleeds, FADECs etc.)

[Denti]

Garuda 421 fits into the category. They had a dual flameout shortly close or within a thunderstorm, ditched the aircraft in a river, only one fatality.

[Sciolistes]

Interesting questions Framer.

What is moderate or even severe rain compared to light rain? I suspect I have never encountered severe precip, and only anything approaching moderate rain at lower levels on approach when there is not a lot you can do about the speed during deceleration and the thrust levers are usually around idle anyway except for the odd level off.

As a result, I have never seen the full procedure implemented, only ever the start switches to CONT.

[lomapaseo]

What is moderate or even severe rain compared to light rain

Imagine flying into a waterfall for several seconds

If you hear the rat-a-tat-tat of hail on the nose dome or windshield you are already too far into it.

Agree that you probably can't thottle back any furthur than the FADEC will allow, but that is one of the fixes the manufacturers have put in.

As for aircraft speed, if you want it to be higher by all means do it with thrust, because high AC speed and low engine RPM are definitely the wrong way to go in this soup

[framer]

Wow there's some great info there, thanks a lot.
The reason I initially put the post up is that I often see descents at maybe 300kts in what I would consider moderate rain with engines at idle.
I guess at the end of the day it comes down to your own personal definition of 'moderate rain'.
I agree with HPBleed that ignition is free.

[RAT 5]

"Keep the aircraft speed down (it's gusty as hell anyway) and the fan rpm up a tad."

Interesting conundrum

[lomapaseo]

Keep the aircraft speed down (it's gusty as hell anyway) and the fan rpm up a tad."

Interesting conundrum

Agree

That's why we have FADECs today

Yes they can be a pain when you're trying to go nice and slow on a descent .. but we do need rain protection in some circumstances.

Similar problem on taxiways when you have to periodically spool up the fan to 60% in near freezing precip/snow.