Moderators: richierich, ua900, PanAm_DC10, hOMSaR
Phosphorus wrote:And no matter how hot, all insects are burned away, and no organic matter blockage.
fr8mech wrote:Phosphorus wrote:And no matter how hot, all insects are burned away, and no organic matter blockage.
We’ve pulled plenty of charred insect carcasses from the tubes if the covers were left off in the spring/summer. Damn bugs only need a few minutes after the probes cool down to get in there and do their thing.
Of course, the probe has to be replaced, but we’d try to capture any organic material and send it off...somewhere...for classification purposes. I wonder if we’re still doing that.
Max Q wrote:One of many good features on the 757/67 was automation of pitot heat operation
No switches exist to turn them on and off, they come on automatically after engine start
More than a few accidents and incidents over the years due to iced up pitot tubes after pilots forgot to turn them on
This was a good idea
Phosphorus wrote:
Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.
fr8mech wrote:Phosphorus wrote:
Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.
Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.
Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.
Phosphorus wrote:fr8mech wrote:Phosphorus wrote:
Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.
Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.
Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.
In Soviet Russia, the switch relays YOU! (/sarcasm)
Soviet designs, where pitot tube heating was activated automatically, relied on landing gear instrumentation. Once load on the landing gear fell, it was assumed the plane was airborne, and pitot tube heating kicked in earnest. Manual switch allowed to ditch the whole thing, and simplify landing gear design.
Starlionblue wrote:Phosphorus wrote:fr8mech wrote:
Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.
Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.
In Soviet Russia, the switch relays YOU! (/sarcasm)
Soviet designs, where pitot tube heating was activated automatically, relied on landing gear instrumentation. Once load on the landing gear fell, it was assumed the plane was airborne, and pitot tube heating kicked in earnest. Manual switch allowed to ditch the whole thing, and simplify landing gear design.
Don't you need the gear sensing anyway for other things, e.g. gear downlock on the ground and spoiler extension. (Granted, those aren't strictly necessary but they're very nice to have.) Did they really remove the gear sensor just to simplify probe heat?