Fuel Injection Icing

[sp6]

Hi all - any ideas on what could have caused this?

Flying an IO360 equipped aircraft with fuel injection, up a coastline after an uneventful over land flight. Weather is:

METAR 131820Z 26009KT CAVOK 16/08 Q1013=

1700' QNH, less than 1NM over the water flying parallel with the coast. 90kts, 2200rpm 6gph. Notice a reduction in power, increase throttle - no response. Full throttle gives no improvement. Excercise Alternate Air - SUDDEN LOSS OF ALL POWER! Alt Air to closed, regain 1900-2000rpm. Fuel pump on, change tanks, cycle mags no change. Declare a PAN and limp home. Power gradually improves but is by no means back to full by landing 10mins later. (still 6gph at full throttle)

Aircraft to be inspected by engineers tomorrow. Initial thoughts are icing to the fuel injection system, and if I'd left the alt air on (hindsight - great eh?) it would have cleared it as carb heat would. Doing some research this evening shows that Alt Air helps with impact ice only and that according to GASCO you can't get icing with fuel injection.

Any ideas? (ps still had fuel in both tanks on landing - before anyone asks!)

[IO540]

Some air path or fuel path blockage.

No way to get fuel icing on avgas at about +12C OAT.

Definitely dismantle everything outside the engine and inspect, including all fuel hoses.

The correlation with the alternate air operation may be a good pointer, or may be a redherring.

[Fuji Abound]

Blocked injector(s), possibly due to contaminated fuel.

Leaking injector diaphragm.

[Red Top Comanche]

When I was training, I had a similar problem on a Tomahawk ( normal carb stuff).

Engine was slowly losing power, selected hot air and it went very rough and i thought it was going to stop. Hot air off and power came back. I Put the hot air back on again but bottled out and turned it off after 5 mins and 1000' loss of altitude and limped back to Panshanger.

Problem was an air leak somewhere, though I don't recall where.

Hope it helps

[will5023]

Hi Get your engineers to also check the fuel return lines, and the tank vents, sounds like a fuel flow/blockage or air in system problem.

Will.

[Mark 1]

It does sound like a fuel restriction of some kind - debris in tank, blocked filter etc.
6 US gall/hr would give no more than about 45% power for a standard parallel valve 8.5 compression IO-360, which at 2200 rpm would normally be at about 19-20" manifold pressure. Full throttle and rich mixture should be around twice that flow rate.
Did the EGT indicate a leaner than normal mixture?
Did you try returning the mixture to fully rich when it happened?
The loss of power given the RPM and fuel flow was probably a lean-cut. I don't know why the alternate air caused a further power loss - possibly it affected the manifold pressure at a given throttle opening.
I would have thought a fuel flow check would give an indication if this was the case.

[Creep Feed Grinder]

Might not apply to your engine.

http://www.lycoming.textron.com/support/publications/service-bulletins/pdfs/SB581.pdf

[moggiee]

No way to get fuel icing on avgas at about +12C OAT.

If you are talking about icing in the tank, true. However, carb/throttle body icing is more likely in warm, humid conditions than cold dry ones.

Throttle body icing is VERY unlikely with an injected engine however, we had a problem with our Arrow where the diaphragm in the fuel [ump was breaking up and the debris was blocking the injector.

[aviate1138]

Had someone put Mogas in [with 5% Ethanol] previously? From your wording it doesn't read as though it was your own machine.

[bookworm]

Excercise Alternate Air - SUDDEN LOSS OF ALL POWER!

But this isn't consistent with induction icing, is it. You'd expect a marginal decrease in power because of the warmer, richer mixture, unless it's a rich cut (seems unlikely). Had you tested the alternate air before flight?

[dont overfil]

I remember reading a report in GASIL many years ago about a partial engine failure in a fuel injected helicopter. After investigation it was decided that the impossible happened and it had suffered from induction icing. I'm sorry I can't remember the details but I think it was about 1989.
DO.

[TwoDeadDogs]

Hi there
Throttle(butterfly)icing can occur in injected engines as I once took part in the retrieval of a force-landed aircraft powered by an IO-540, which had made a descent thru cloud, aftre having encountered icing conditions.When the crew popped out of cloud, the throttle wouldn't respond and all they could get was idle power.When the cowlings were pulled off, the remains of ice could be seen in the air intake and the engine was soon able to be started and it ran normally.
I would also go along with the suggestion about checking the fuel manifold, as I have also encountered a loss of power associated with a diaphragm failure in the flow divider on an IO-360.
regards
TDD

[IO540]

remains of ice could be seen in the air intake

This is nothing more than structural icing, possible in any IMC between 0C and roughly -15C.

The argument about fuel system icing in injected engines is whether one can get it due to the gas expansion. I don't think one can.

There would not have been gas expansion triggered cooling in the air intake.

[BHenderson]

We had a Mooney land at Newcastle last year with suspected induction icing. The pilot had overboosted the engine trying to maintain power. It lost most of its oil through the turbocharger and I believe most of the cylinders needed to be replaced. The conditions were perfect for normal carburetor icing. The Mooney was in VMC. The engine died on the runway.

I think people rule out icing far too quickly. Have people read the articles on clear air ice formation under the anvil of large thunderstorms in turbine engines?

My theory here is that induction icing formed at the butterfly.

[Captain Smithy]

BHenderson, I have read articles on flying under the anvil of CBs and from what I have read it is not a good idea... there was an incident with a B757 at Palma a while back (couple of years ago perhaps?) that flew under the anvil of a CB just after takeoff and was damaged by hail.

Smithy

[Wrong Stuff]

Induction icing is not unheard of in the older M20K turbocharged Mooneys, but the conditions conducive to it are very cold temperatures in visible moisture and the icing forms on the induction air filter. Opening the alternate air system or descending into warmer air restores power. To alleviate the problem, the factory offered replacement automatically opening alternate air systems. The main region the reports of induction icing problems came from were in Northern Canada during the winter. There are no documented reports of induction icing problems in other areas, including those where carburettor icing is much more prevalent (such as IMC).

If the Mooney really was suffering from significant induction icing, the air supply would be being throttled and power output would consequently be low. I can't see how the pilot could then overboost the engine. Of the potential icing problems, it sounds more likely he was suffering airframe and prop icing and needed the extra power to make up for the drag and deformation of the wing and prop aerofoils. Given that conditions were VMC, that would appear not to be the cause. More probably there could have been some blockage in the fuel supply which would have allowed him to run at higher power but with a very lean mixture and high EGTs, but that would have been nothing to do with icing.

[Fuji Abound]

I am still going with blocked injector(s).

:confused:

[sp6]

Sorry for the delay in replying, but the engineer's inspection revealed a blocked injector.

I did try fully rich but it gave a further drop in rpm. The Alt Air was tested on the run up before TO and it gave the normal slight drop. The fuel was from a regularly inspected supply, tested during the A check that morning, the aircraft had flown approx 2 hours prior to the incident on the day and the aircraft has been fairly busy over the last few weeks.

Thanks for your responses - I guess it answers the original question about ice!

cheers

SP6

[IO540]

On an IO360, one blocked injector does not account for the symptoms in your first post, sp6.

A single blocked injector would cause rough running, with a lot of vibration, but not what you got.

You may find other stuff elsewhere...

[sp6]

The message about the injector was passed on to me today, I haven't been back to the airfield to talk to the engineer in person. Before I do go back, I'll certainly be reading up on how injection systems work - my old text books just show carburettors.

The engine continued to run smoothly, with the reduced power. and in response to an earlier post, only AVGAS from a certified source is used for that aircraft - no way could it have been MOGAS and no one uses the aircraft for touring so it never leaves its home base.

I'm just glad 2100rpm was enough to keep me flying and enough for a slow climb to give me 2500' qfe when I got to the field. Phew!

[IO540]

Not a blocked injector, definitely.

If you want to see what one blocked injector does, pull out one of the plug leads, and do a mag check. When the cylinder whose plug you pulled has the other plug not firing as well, the engine shakes like hell. You can't miss it, especially at 2000rpm.

But you could fly like that, in an emergency. There is a loss of power but not enough to stop you flying. The engine is very unlikely to actually fall off.

You could have had all injectors partially blocked but then you have to wonder what else has got bunged up with crap... IMHO it's a problem elsewhere.

[IFollowRailways]

I agree with IO540 - The symptoms you described do not seem to me to be a blocked injector as I can personally testify from an experience a few years ago!

I was flying with a glider pilot acquaintance in the other seat - He was doing the flying whilst I was idly looking out of the window - All of a sudden the power just evaporated and there was silence from the front. My friend really was flying a glider now.............

To cut a long story short, whilst looking for the trim, he had turned off the fuel cock which was located between the front seats. When I (eventually - thats what makes it a long story!) restored fuel to the correct place the engine ran like a dog - coughing, banging and generally horrible - It ran so badly that I nearly continued into the field I had selected when we were a glider! After experimenting I found I could maintain height and so continued into a nearby strip.

Upon investigation, all sorts of crap had been drawn through the fuel system and I had one blocked injector and all sorts of debris floating about that may have been partially restricting fuel flow to the other injectors.

[Fuji Abound]

If you want to see what one blocked injector does, pull out one of the plug leads, and do a mag check. When the cylinder whose plug you pulled has the other plug not firing as well, the engine shakes like hell. You can't miss it, especially at 2000rpm.

Perhaps partially blocked is a better description.

Very recently an aircraft I fly had a problem that was diagnosed as a blocked injector. It manifested itself as a consistantly higher EGT on one cylinder and a higher CHT at high power settings on the same cylinder. The engine other wise ran smoothly and there were no other symptoms. In fact without the engine managing parameters the problem would not have been noticed. Certainly there was no shaking at any power setting.

On the other hand when I had a split diaphragm the symptoms were very much more as you describe albiet the engine ran rough as opposed to shaking itself to bits.

Finally on the occasion there were two dead (or perhaps badly contaminated) plugs in the same cylinder even at low power settings the engine was very rough with no EGT and CGT readings on the cylinder in question.

Two different engines and three different occasions (one six cyliner and one four) and I guess in a four cylinder engine the symptoms are going to manifest themselves in a more pronounced way.

[IO540]

Yes, I would suspect either something in the fuel servo has gone, or there is serious fuel contamination.

Reminds one of that never-ending BA 038 thread in the Rumours section :) Must be up to 250,000 posts now, a lot of them very interesting, but it doesn't look as if anybody has a clue as to what caused that one.

[SNS3Guppy]

Flying an IO360 equipped aircraft with fuel injection, up a coastline after an uneventful over land flight. Weather is:

METAR 131820Z 26009KT CAVOK 16/08 Q1013=

1700' QNH, less than 1NM over the water flying parallel with the coast. 90kts, 2200rpm 6gph. Notice a reduction in power, increase throttle - no response. Full throttle gives no improvement. Excercise Alternate Air - SUDDEN LOSS OF ALL POWER! Alt Air to closed, regain 1900-2000rpm. Fuel pump on, change tanks, cycle mags no change. Declare a PAN and limp home. Power gradually improves but is by no means back to full by landing 10mins later. (still 6gph at full throttle)

Aircraft to be inspected by engineers tomorrow. Initial thoughts are icing to the fuel injection system, and if I'd left the alt air on (hindsight - great eh?) it would have cleared it as carb heat would. Doing some research this evening shows that Alt Air helps with impact ice only and that according to GASCO you can't get icing with fuel injection.

Any ideas? (ps still had fuel in both tanks on landing - before anyone asks!)


Loss of power is the first clue, but we're not given enough information. Did you adjust mixture or check your CHT/EGT at the time? The first thing that springs to mind is an induction leakage. If you experience an induction leakage and lose power (as you will), you'll have an imbalanced mixture to one or more cylinders. Opening alternate air with warmer airflow will increase these effects and produce a rough engine.

A plugged injector, partially or completely, may or may not produce roughness. Very often the only indication will be an increase in indicated fuel flow, where fuel flow is measured by differential pressure and not actual flow (depending on the system in use, of course)...what appears to be using more fuel is actually using less, and is often mistaken for something else entirely.

I've seen alternate air doors fail and block the induction before, or fail to seat (some use a magnetic latch which fails, others have mechanical control all the way through their range, and yet others may be opened in flight, but cannot be closed or secured until back on the ground...again, depends on the installation). I worked for a corporate department years ago in which an aircraft was lost (and all aboard killed) after one engine failed, and when alternate air was applied on the second, the door failed and blocked the induction...causing the loss of the second engine.

I've also seen ducting collapse which produced alternating and intermittant roughness or failure. This is more common in semi-rigid ducting such as SCAT hose, but I've seen it in injected and carbureted installations. Pull the cowl and look at the hose, it appears intact. Under low pressure or certain operating conditions, however, it can collapse.

The most common source of induction leakage in injected installations is the flexible couplings in the induction, typically hoseclamped onto the metal portions extending from the cylinders. As these age and are affected by heat and the clamps, they tend to develop leaks around the clamps. The net effect is uneven airflow to one or more cylinders, and depending on the fuel metering system in use, this can greatly affect the mixture to one or more cylinders. This may or may not show up as an obvious EGT problem, depending on whether you're using single point or multi-point EGT measuring (single point hides a lot of problems), but you an certainly experience a rough engine and cylinder damage, especially if you're already operating close to peak at high power settings.

Some talk has been made of icing. While icing sounds good, this isn't a carburetor, and doesn't ice like a carburetor, and doesn't clear like a carburetor. The original poster seems to be applying carburetor heat theory, believing that if he had induction ice in an injected engine, then using alternate air would melt the ice and cause a rough running engine. The problem is that while carburetor heat puts warmer induction air through the carburetor venture (where the ice is located) and thus melts it or prevents it's formation, that isn't true of the injected engine. In the injected engine, alterate air opens a door which merely provides an alternate air path.

I don't believe the original poster differentiated between the Lycoming IO-360 or the Continental IO-360. Each uses a different fuel system and induction; the induction is part of the fuel system and is used to determine the amount of air metered past the throttle body; therefore the two are tied together, but the diagnosis and troubleshooting are different.

A possibility for the loss of power in the first place was a problem with the alternate air door. Airworthiness Directives apply to certain installations regarding the deterioration, deformation, or failure of alternate air door asemblies. Cracks and distortions in the alternate air door are not uncommon, along with failures of the door, or hinge assembly, or actuation assembly (often a simple rigid cable). Parts of the door assembly can break free, or the entire door, and block the induction causing a partial or complete power loss. In some cases where a power loss occurs, a change in power setting may alleviate the problem, but often not.

A mechanical failure of the filter element in the primary induction path is also a possibility, especially if this partially occluded the throttle plate. Icing that blocks induction on an injected engine is typically at the filter, upstream of the throttle plate, rather than on the throttle plate, and it's for this reason that alternate air is provided...not to melt the ice, but to bypass it completely. If the filter becomes blocked, it can be by passed. If the filter fails, however, then alternate air may be of little use, or may contribute to the problem, depending on where and how the blockage occured.

When going to alternate air, you're going to need to make a mixture change. If you're already operating in a condition close to the operating limits (overly rich or overly lean), then you're in a position to cause the engine to quit or run rough until a mixture change is made.

The original poster stated that one can't get icing with fuel injection...this isn't true, but the icing isn't quite the same as what one gets with carburetion, and it's more tolerant.

Some induction systems also use more than one source for alternate air. Typically a source may be provided upstream of the throttle plate, but one is often provided down stream of the throttle plate, too; this is often an automatic emergency door which may or may not reset, and takes away some throttle control because of it's location. Sometimes referred to as a "suck door," it operates based on differential pressure between the induction and ambient, and is generally magnetically held closed. It's sucked in, to provide airflow; various installations are used in different aircraft and not all aircraft utilize them. A failure of this door to the open position can also cause some of the problems described.

Another thing to consider in your preflighting and subsequent use of alternate air is what's near the alternate air opening...which is generally located within the cowling. I've seen bird nests show up there which can then be sucked into the induction and cause an unrecoverable failure when alternate air is used, as well as mouse nests or other debris...check "under the bonnet or hood" when you can. Your preflight can't be too thorough.

I've seen bird nests removed three and four times in one day from the same engine...they can build them that fast; I've seen them built in hot engines. That airplane you flew in and parked an hour or two ago while you were having lunch may be a completely different airplane when you get back to it. Check it thoroughly.

The main thing is that you got back to the ground safely. Hopefully when it occured you immediately maneuvered to a place where you could execute an immediate emergency off-field landing, and kept yourself in a position to do so until you made it back to the airport. Remember that it's never a matter of if you'll have an engine failure. Only a question of when.

[IO540]

I've seen bird nests removed three and four times in one day from the same engine...they can build them that fast; I've seen them built in hot engines. That airplane you flew in and parked an hour or two ago while you were having lunch may be a completely different airplane when you get back to it. Check it thoroughly.

Not likely in the UK. Nowadays, British birds are often too fat to even climb into the cockpit.