Gooberman

@MCCCANM Nicely explained.! There is a check valve at the PCA inlet that if working should prevent back flow but it's procedure to disconnect it anyhow.

I find myself frequently explaining the air systems of an airplane in replies, so let’s do a post to try & answer questions. I’ll base everything on the 737, but most jets are similar. At the gate as you board, air comes from one of two sources: Ground Air (called PCA, or Pre-Conditioned Air) which is basically a big air conditioner mounted on the jet bridge, or the Auxiliary Power Unit (APU) which is a small turbine engine in the tail, providing both electrics & pneumatics to the jet when the engines are off. I usually find the PCA gets too warm in the summer. It pumps out good air, but for whatever reason the jet gets warm. It might be because it travels to the jet via a big yellow hose that attaches to the belly & that hose is out in the sun. I don’t know. In any event, the APU pumps out a little more air than the PCA, and I can control the temperature better. At my airline, they don’t let us run both APU air & PCA at the same time, as they fear over pressuring the ducts, but I hear other airlines do. I have done it in the past & watched a duct shut itself off…thankfully it came back on when I shut off APU air. Anyway, when you disconnect PCA at the gate, you switch to APU. They also remove ground electrics at that time, which the APU takes over for as well. (The APU air path is not included in the diagram below, but it’s the best I can find) Then we push back from the gate. During engine start, there is a brief period that we divert APU air to the engine. This spins the engine, which allows us to introduce fuel & ignition. Once the first engine is started (the right one, number 2), we take air from it to supply the cabin. Pay attention here: even though the APU is not supplying air to the cabin during this moment, you’ll notice some air is coming out of the vents, albeit at a lower pressure. We’ll talk about that in a second. For simplicity’s sake, just understand the engines supply cabin air the rest of the way. We can use the APU, but we shut it down as soon as the engines are running. No need to waste fuel. All of these air sources go through a process of cooling via a heat exchanger (I’m simplifying), except the PCA…because, as it says in the name, the PCA is pre-conditioned. Anyway, once brought down to temperature, it goes into the “Mix Manifold”. The Mix Manifold is where the outside air meets the recycled air, taken from the cabin. Remember how there is still air coming from the vents when the APU air is diverted to start the engines? That’s because the “Cabin Recirculation” fans (there are two) are always on & pulling air from the cabin to go into the Mix Manifold. The “Recirc Fans” are just left on at all times, unless we have smoke in the cabin & need to stop circulating it. They also turn off automatically when we shut the battery off on the last flight of the day. They can turn themselves off under some conditions of the engines, but that’s not meaningful to your understanding. Just remember that those switches are left in “on” & we don’t touch them unless an emergency checklist tells us to. So, the Recirc Fans are constantly pulling air from the cabin through a big HEPA filter. They push that air into the Mix Manifold, where it mixes with PCA, APU or engine air & gets distributed to the cabin. On landing, we start the APU back up. It will take over air & electrical duty from the engines so we can park at the gate, then reconnect PCA & ground power. Once they are connected, the APU is shut down. You may wonder what the term “PACK” means in the diagram. This refers to the air-conditioning “packs” for each engine. We just call them packs, but it’s where the heat exchangers I referred to earlier are (it’s more complicated than that, but it won’t help your understanding). Now, it’s possible to have the engines off, no PCA & no APU at the gate. That’s not the norm, but even in this scenario the recirc fans are still pushing air. It just doesn’t get cooled, so the jet gets hot. Hope that helps!

@mattvanswol And no one has gone to jail over it either.

Don’t EVER forget that FEMA kicked ENTIRE FAMILIES out of their hotels and into the ice and snow in Western North Carolina… …while giving $59,000,000 to let illegal immigrants live in luxury hotels in New York City AND THEN THEY LIED TO US ABOUT IT FOR MONTHS!!!!!

@BuzzPatterson I bet blood tests scrapped off the exit guide vanes show he was all drugged up...

Infrared video showing the Frontier jet hit the person. He looks pretty chill to me. The poor pilots had no chance to do anything. They probably didn’t even see him at night until the last moment.

@9mmsmg Just hope that only one of your pilots is a DEI hire and not both...

Flying can be very stressful. As we're getting ready to head to the airport, I have a quick prayer request. Could you please say a quick prayer that no Spirit passengers purchased a discounted Delta ticket? I'm just not up for that today.

@Mrgunsngear Pretty bad security....

A Frontier Airlines Airbus 321 engine sucked a person into it, killing them on the runway at Denver International Airport late last night 👀🔥 Avoid walking on active runways accordingly... #CityLife #denver #frontier #FAFO #airbus #physics #flying #urban #fail #learning #education #flying

@CBSNews So if I broke into the CBS building and walked around I would just be a "pedestrian "?

"We just hit somebody": Audio captures the moment a Frontier plane hit a pedestrian on a runway before a takeoff in Denver. cbsn.ws/3P61lYP

@BuzzPatterson I've seen the competence go down so much in all departments at the airline I'm at for over 35 years.

FLYING & DEI: IT KILLS As some of you know, in addition to my career as an Air Force pilot I was also a commercial pilot for Delta Air Lines. Twenty years in the USAF and 16 at Delta. Throughout, I was impressed with my fellow pilots whether military or commercial. My peers were solid, the training was exemplary, and the maintenance on our aircraft was the best. I was blessed to safely operate aircraft into and out of 70 countries over 35 years and over 10,000 hours of flying time.  However, as our society evolves, for better or worse, many industries continue to promote diversity, equity, and inclusion (DEI) in the workplace above and beyond operations that are founded solidly in safe and efficient operations. Among the several industries that have taken this on in the face of the risks is the U.S. airline industry at the direct expense of the commercial flying public. It has indeed introduced questions and concerns about the safety and competence of the flying industry. One of the most recent incidents occurred in January 2024, when a United Airlines flight with a diversity “new hire” bent metal on a landing on their training flight. “Bent metal” like taking it out of service. That’s not cheap for United nor is it an endorsement for future paying United passengers. The incident led to an investigation into the company’s hiring practices and questions about the hiring practices and training standards for pilots who are less qualified than others. It was one of many instances that have occurred recently where the potential risks of prioritizing diversity over experience and competence have been highlighted.  Another issue that has recently been brought to light is the potential for discrimination in the hiring process. When I was leaving the Air Force and interviewing with the various airline companies, I was surrounded by experienced pilots from all walks of life. But they had decades of experience and they’d been through the shit. Mostly military but not all. Today, when you walk to your gate, you’re possibly getting a pilot, a flight attendant, or a mechanic who was hired based solely on diversity, equity, or inclusion. Airlines are setting diversity hires above qualifications at your expense.  When you board your aircraft with a ticket you’ve paid dearly for, what are you looking for in your aviation experience? I know when I board one now with my family, I know exactly what I’m looking for. Experience and competency. In response to the concerns that DEI initiatives are essential for promoting a diverse and inclusive workspace, I understand that. However, I firmly believe that safety should always be our primary concern and goal. Any and every attempt to ignore that should be eliminated and squashed forever. Otherwise, we’re going to start seeing planes fall out of the sky and innocent people die. As a member of the flying public, what do you think?

@Mrgunsngear @SecWar Agreed. Just like the politicians and doctors who lied and forced people nothing has happened yet so nothing will.

Good update on revising negative actions - that's a no brainer. That said, EVERY SINGLE flag officer who held a command position and issued this unlawful order needs to be criminally tried for their crimes under the UCMJ. Why would anyone who got out because of these criminals want to serve under them now when they have even more rank? It's illogical and not charging them is immoral. They knowingly and willfully broke the law for political or personal reasons, that should be unacceptable but as long as you let them serve without charges then you're telling them it's 100% acceptable and you are continuing to reward them for it.

The Biden administration’s experimental COVID-19 vaccine mandate was wrongfully forced onto our warfighters. It was unjust, and we are doing EVERYTHING we can to make it right.

@Mrgunsngear Imagine if the cop called him "boy"?

TN democrat Rep. Justin Pearson did this today following a redistricting vote 🤨 "Move the fuck back, boy!! The fuck is wrong wit chu?! You stupid motherfucker!" -Rep Pearson #CityLife #tennessee #cops #JustinPearson #racism #crime #nashville #enrichment #democrats #urban #3rdWorld

@NBCNews Why do people even watch and read you anymore? That headline didn't slip by an editor

Kyle Rittenhouse, who gained fame for opening fire at a 2020 civil rights rally in Wisconsin, was hospitalized after he was bitten by a venomous spider, the noted firearms enthusiast says. nbcnews.com/news/us-news/g…

@FLVoiceNews @ByronDonalds Quit picking sides or more people will unfollow you. I'm getting real close

Byron Donalds unveils major government accountability plan to make Florida the most transparent state in America Donalds also released a new campaign ad highlighting President Trump’s endorsement calling him “a fighter” who will be a great governor @ByronDonalds: “Florida taxpayers are the owners of the government, and they deserve to see exactly how their money is being spent." flvoicenews.com/byron-donalds-…

@HLC_actual As a mechanic I joke sometimes with the pilots when a pylon latch on the 757 eng sometimes pops open. They call us out to close it and I always ask which on is a navy pilot.

Yall ever come down so hard in a plane you immediately assume your pilot is former navy? Like FUCK Carl this 737 doesn’t have a tail hook chill man.

@Mrgunsngear I always wonder about the bodies. Are they never recovered? Just left out there by both sides?

The Ukrainian defense minister announced earlier today that, *IN APRIL 2026 ALONE*, they killed 35,000+ Russian soldiers with drones. The number of dead & wounded on both sides of this war is one of the most under-reported (by western media...) stories of this century. Avoid modern war accordingly... #war #ukraine #russia #drone #drones #senseless #nato #technology #FPV

@GuntherEagleman It's called TDS.

LOL! Barack Obama reveals that Trump has caused ‘genuine tension’ in his marriage to Michelle: ‘It frustrates her’

IT’S OFFICIAL! DeSantis just signed Florida’s new congressional map into law. Republicans are expected to gain 4 seats

@DonutOperator @TheAKGuy Did he ask to see your medal too?

I’m not even in Japan for 24 hours and someone walks up and asks me if I’m @TheAKGuy

@nicksortor As someone who was stationed there i lived it. It's a great place for an 18 year old to experience. I do remember though how the German government always charged us for everything. That should be fixed atleast

🚨 BREAKING — IT’S OFFICIAL: President Trump is WITHDRAWING 5,000 US TROOPS from Germany after Chancellor Merz criticized 47’s Iran operation Good! Tell NATO to take care of themselves. We don’t need them. BRING OUR TROOPS HOME!

@TaraBull Crashes have nothing to do with it.

Spirit Airlines is preparing to shut down after Trump bailout falls through. Historically, Spirit Airlines has not recorded any fatal passenger crashes since beginning operations in 1992. Many believe they deserve a bailout. What do you think?

@WallStreetApes Fine. Pay that for some fancy dessert labeled coffee. But if I want a regular black coffee it should only be $3

Starbucks CEO defends a cup of coffee costing $9 He says the customers needs to just not think about it as a $9 cup of coffee, you’re paying for the “experience” of getting a Starbucks coffee “In some cases a $9 experience does feel like you're splurging, and then what that means is we have to make it worthwhile.” He says Starbucks customers “want to have a special experience and regardless of what your income level is, in some cases, a $9 experience does feel like you're splurging — well, this is a really affordable premium experience” How out of touch could a person possibly be…

@Mrgunsngear But the atf never goes after people like this?

I've watched this video 4 times. Every time I watch it I notice another thing that makes me laugh 😂 If you see this crew on the range, walk away accordingly.... 👀 #stick #ar15 #NoBrace #sideways #magpul #WTF #sight #laser #fail #slippers