This is an excellent piece of communication from Mr. Randazzo on behalf of PMDG. Honest, open, to the point. Sounds like they (and other 3rd party developers) were caught off-guard by the announcement, just like the rest of us.
I appreciate this memo. And I don’t envy their position. They are going to have to scramble a bit to keep up with this situation as it evolves. And I’m sure it will require pulling development and testing resources off other projects when early releases of the new version come out. It’s just going to be something we all have to deal with. And I hope PMDG doesn’t get too much pressure and blame from the customer base when those resources are redirected. It’s not their fault. They, and other development organizations, are going to be in a tough spot in the coming months trying to keep up with all this. Testing for and supporting products on two releases isn’t ideal. But that’s the world that we are about to all live in for a time.
Yeah. The MEL allows dispatch without APU with very few considerations. It’s also not an urgent repair. The MEL allows for 10 days to rectify the fault (Interval C).
Dispatching without APU is annoying but it’s not a big deal if you’re not flying ETOPS (within 427nm from suitable landing airport on the -800) and it doesn’t affect CATIII operations. It doesn’t create any flight limitations like other MEL items would. For example dispatching with 1 PACK INOP would limit your cruise level to FL250.
Dispatching with APU INOP only means that we’ll need to start one engine on the stand with ground start and then do a cross-bleed start for the other engine after pushback. Without APU we don’t have air conditioning on the ground so if the airport doesn’t have ground AC units the cabin will get very hot during the turnaround.
Wasn’t starting the APU one of the key things that Captain ‘Sully’ Sullenberger did when both his engines were taken out by a bird strike, in the famous landing on the Hudson River?
I understand that the investigation named that as one of the key decisions taken by the flight crew.
Without the APU, i understand that a lot of the avionics might not have been available, making a safe ditching even more difficult.
Makes sense that he would do that. Not only to supply power to the avionics but hydraulics to the flight controls and bleed air to try and restart the engines.
You are correct and it raises a very good point about aircraft maintenance. Modern aircraft are extremely safe in large part because of system redundancy. A Minimum Equipment List (MEL) or any other approved list of inoperable equipment allows the operator to continue to operate the aircraft with reduced redundancy. The decision factors being that the more important the equipment is to safety of flight, the faster it must be repaired and functionality restored. The MEL system is designed for commercial operators ostensibly to allow them to continue to make money with an aircraft despite maintenance issues existing. For the operators, this makes great financial sense. For the passengers, no matter how you cut it, they lose some of the safety margin that an otherwise fully functional aircraft would have.
In reality, as long as you are flying on a reputable airline, the aircraft is perfectly safe. There are far bigger things to worry about in life than the maintenance status of your airliner.
Yes but it doesn’t mean that you wouldn’t be able to fly the airplane without APU with a loss of both engines and hydraulic power. The 737 is different to the a320. Remember the 737 has manual reversion. If you lose all hydraulic power you can still control the airplane without any hydraulics because the controls are linked to the control surfaces through cables (check out the QRH checklist “MANUAL REVERSION or LOSS OF SYSTEM A AND SYSTEM B”). Airplanes that do not have linked controls like the 737 usually have a RAT that supplies hydraulic power.
The avionics that keep working after a total loss of generators is enough to fly the airplane. Remember we still have sby power powered by the two batteries for at least 60 minutes.
Luckily both a full loss of hydraulics and generators is something you can simulate in the 737 PMDG so there’s a nice challenge for you.
No need to wonder. That’s what the MEL is for. It’s very restrictive for certain items and no so much for others. There are INOP items that let you dispatch with certain conditions (like a cruising level ceiling cap etc) and others that simply NOGO the airplane.
Airplanes are incredibly robust and this APU thing is just one of those things. If your APU goes inop in a station without engineering you just need to dispatch without one. In airlines with big budget the airplane wouldn’t be without APU for more than 1 or 2 days (or even less if you’re at an engineering base where they have APUs laying around and can swap it overnight). The MEL allows a rectification period of 10 days in case of the APU.
On occasion, I’m seeing “zone temp” alert lights illuminated (might be wrong on the phrasing). I can clear them via the reset button on the panel but am curious as to what is causing the alarms in the first place. Any ideas?
What purpose does entering runway length and elevation into the HGS system serve? Just curious. Also, does the FMS provide runway elevation data? I can get RWY length, heading and ILS freq from the system, not elevation (I know I can pull this from the charts).
Every approach chart shows you the length of the LDA and both the elevation of the threshold (Touch Down Zone Elevation TDZE) and the airdrome reference point (ARP).
Yes, I was aware of that (as I mentioned above), was just curious if the FMS provided that data somewhere in it’s system, also trying to figure out what purpose is served by inputting it (and RWY length) into the HGS controller.