Smell gas?

[Crepello]

On Saturday afternoon, I rented a 172 to thrash the pattern for a while. Preflight was fine, ditto the runup, and all was going smoothly as I turned downwind for the first time. I've about 150hrs TT.

Suddenly, there was a strong smell of unburned avgas in the cockpit, also noticed by my passenger. I got clearance for a full stop, made a short final and landed without incident. We taxied to the FBO and shut down. The smell remained strong, especially near the left footwell and wingroot air vent. I'll swear there was a smell of electrical burning when I shut down, but this could just have been my heightened 'alertness'. We didn't dawdle...

Checked the plane with a CFI but found nothing - no leaks, no scorches. Turns out it had happened before on this plane but they couldn't trace it. It's since flown again without incident.

Questions:
- Anyone had a similar experience?
- Should I have declared an emergency prior to landing? (Seemed excessive at the time but I don't know the risks. Field was quiet so I knew there'd be no problem getting a full stop landing).
- Should I have shut everything down and come in dead-stick? (had plenty of height) My prime concern was a cabin fire - would imagine the instrument panel has plenty of ignition sources.

Interesting self-learning though. Next time I'd try harder to identify the source, unlatch the doors on landing, and change my preflight briefing to "if you see or smell anything unusual..."

Edit: Thanks slim_slag, good point: The previous renter flew 1.6 hours after topping the fuel off, so the tanks were about 60% full. He didn't report any problems.

[Final 3 Greens]

I once had avgas leaking out of the LHS roof due to a problem with the cross feed between the tanks on a C172.

Only happened once, but it was rather disconcerting.

The smell was intense and small drops of avgas were falling on me.

This happened during taxi for departure, so a swift 180 back to the parking spot was executed and the a/c removed frm service for repairs.

[slim_slag]

How full were the tanks when you departed?

[Gertrude the Wombat]

I think I'd have mentioned the smell of petrol. I'm not sure I'd have declared an emergency, but they'd quite likely have sent the fire engine after me anyway, which I'd probably have welcomed.

On the other hand I have been known to refuse to fly aircraft which turned out to have nothing wrong with them ("oh yes, that one does that sometimes, the engineers can't find out why but it doesn't seem to do any harm").

[Cusco]

Only time I've had a strong smell of avgas was just after take-off from the strip, so I came back PDQ.

Turned out I'd tucked the fuel strainer into its rightful place in pax footwell pocket, but I hadn't emptied it completely: there was about 4cm of avgas in the bottom of strainer.

No idea how it happened but you can bet your sweet bippy it hasn't happened again.

Safe flying.

Cusco

[AMiller]

Hi there, i'm a military pilot but was just browsing through the other threads......

Answers -

1) Yes whilst solo (tucano) recovering medium level into Linton at about 200kts under radar service I smelt similar. Tried carried out the "fumes in the cockpit" drill. But, as you can imagine, at that speed in cloud keeping an eye on the intruments was more important!!

2) You should most definitely have declared an emerg. Not sure what your airfield services are but at Linton they were there waiting for me on the ORP and followed me down the rwy.

3) I considered setting up for a forced landing pattern, we train these everyday. But, given the cloud base was around 1,000ft this would have not worked. If you were operating at height (at least 1000ft above high key (to be safe) AND the airfield was clear with good met then yes you should have considered it.

Sorry if this is not helpful, just my 2p's worth.

[Fg Off Max Stout]

Also a military pilot.

Anytime you feel twitchy with reasonable grounds you should call a pan (in your case) or mayday, as required. You can always downgrade or withdraw it if the situation improves. You'll get the full attention of the tower and the bloodwagons until you're safely down. You'd feel a pratt sitting in the burning wreckage thinking 'I wish I'd called a pan'.

Personally I wouldn't recommend shutting down and deadsticking it in. I think you're just adding to your problems. Far better to make a sharpish controlled landing under power than to shut down the engine, try to glide and stall/spin in or land in trees/hedges/hillsides/brickwalls as many have done in the past. It's very difficult to make a judgement on something that is essentially subjective without being in that cockpit but I think aviators with more experience than me might concur.

So what do you think, chaps?

BTW, if you do an aerobatic sequence in a Chipmunk and DON'T smell avgas, then something's wrong.

Edited for spelling avgas with a tur. Haven't used pistons for a wee while.

[Genghis the Engineer]

Seen the same as F3G on the ground in a C152, half tanks. Refused to accept the aircraft!

G

[Lowtimer]

BTW, if you do an aerobatic sequence in a Chipmunk and DON'T smell avtur, then something's wrong.

That would be one of those new turboprop Chippies, would it?

(Yes, I know, nobody loves a smart****:} )

But to your main point, yes, I think it would be better not to add a second emergency by shutting down unless you have a further reason, or things got much worse, e.g. raw fuel visibly sloshing about inside the cockpit

[Mike Cross]

Smell of Avgas not unusual in the Luscombe.

It has wing tanks with independent fuel cocks going to a tee and then to the gascolator.

Being an old aeroplane it naturally flies on the chinese manner (Wun Wing Lo) which can result in fuel cross-feeding from one tank to the other if both fuel cocks are on. If they are both pretty full then it can overflow and get into the wing structure.

The remedy is to feed from one tank only in our case.

Mike

[stiknruda]

Very easy to get fuel into the Pitts cockpit when filling it and just as easy to spill smoke-oil when filling the smoke tank.

Best to refuel with the canopy cracked open to allow fumes to evaporate.

If aerobatting with full-ish tanks, prolonged inverted can have that fumey smell.

But as long as you expect it it is not so frightening.

In the case such as the one outlined above, I'd have panned and landed asap.

Stik

[Circuit Basher]

Generally concur with all of the above (declare pan and keep the engine running), but would also add that there is a dilemma when smelling AVGAS in the cockpit to try to avoid using ANY electrical switches (including the PTT as depending on your comms kit, this may operate a transmit relay).

You run the risk of making a spark, which could create an emergency all of its own! Also, noone seems to have clearly stated (although have implied) the need for *immediate* ventilation of the cockpit, unless it is suspected that the AVGAS source is external.

[Fg Off Max Stout]

Good point CB. Fumes in cockpit -> get some ventilation.

[Say again s l o w l y]

172's seem to particularily prone to this sort of thing. Often it's something like a blocked drain or a slight crack in the filler neck.

Usually the fumes enter the cockpit via the air vents since they run along the leading edge in front of the tank. For some reason I've always found that the left tank is more prone to this, don't ask me why!

There only needs to be a tiny amount of vapour for the smell to be very strong, but it is alarming. Remember that sometimes the smell is not from the a/c, but from you, especially if you've just refuelled and have spilt some Avgas on yourself (or trodden in some)

In this regard AVGAS is alot better than AVTUR, since that doesn't evaporate away so quickly and it really does smell awful!

Whilst the smell of fuel is a pain and a worry, you are unlikely to turn into a ball of flame. It isn't a massive problem there and then, unless it is so bad that you are choking and your eyes are watering. Obviously it needs investigating ASAP and getting down sooner rather than later would be sensible, but it would rarely be an emergency.

I would be more worried about the physiological effects of the fumes (headaches, nausea etc.) rather than thinking we were about to burst into flames.

[Yorks.ppl]

During my training I flew a 172 for a while, I regularly smelled avgas but my instructor said it was always like that and it was ok.
Can one of you technical chappies (genghis?) enlighten me as to wether it is ever acceptable to fly a plane that smells of fuel inside or if it should be a zero tolerence thing.

I guess S.A.S partly answered my question whilst I was typing:O

[tmmorris]

PA28s seem to be prone to leaking primers, in my experience, with similar results.

Tim

[Crepello]

Some great replies folks - very much appreciated.

SayAgainSlowly's description follows my own reasoning; a small leak of fuel into the left wing or suchlike. I ruled out the internal causes - fuel tester was empty and I hadn't topped-off. Wasn't too concerned about inhalation as we were in the pattern when the 'aromatherapy' began, but on a different day...

I take FgOffMaxStout's point about calling a pan, and would probably do so if it happened again. But I'll be opting for a different acft next time.

Cheers, Crepello

[Phororhacos]

We used to operate a group owned C172 that leaked a small amount of Avgas from the primer, despite having it looked at by the engineers once or twice. Always a faint smell of fuel in the cockpit. Despite this, still found cigarette butts in the ashtrays on occasions , (and we had a no-smoking sign).