PPRuNe Forums - View Single Post - MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Old 3rd Dec 2019, 23:10
  #4242 (permalink)  
Join Date: Nov 2015
Location: Bay Area, CA
Posts: 65
Originally Posted by gums View Post
Way off topic now, are we?
Well, having done hundreds of rolls and "things you have not dreamed of", to borrow a line from High Flight.
You can roll easily without initially getting the nose high if in a small, or nimble plane. Problem with the big boys is inertia, and nose will dig in easily. Hence nose high to start. OTOH....

The ET flight had extreme nose down trim, so every degree of roll from normal erect provides less of a lift vector below the horizon, right? Eventually, all of its lift vector is above the horizon when completely inverted. So a technique I used on most jets to avoid the nose high entry was applying forward stick and a touch of nose down trim as bank angle increased past 90 deg, and maybe some top rudder until over 90 deg of bank. Could literally roll within 20 feet of initial altitude, and the T-birds and Bluers and Arrows and Snowbirds show this every performance. So Denzel's manuever is theoretically possible. And worry about motors quiting later. 737 flies O.K in glider mode due to the mechanical connections, right? We need "wonkazoo" to comment, as he flew aerobatic demos all the time.

The Alaska folks should get a post humous medal of honor for even trying the Denzel trick, as they had nothing to loose. And IMHO biggest mistake was not trying to land when things started acting up. Of course if they didn't turn off the electric trim motor, then they could have lost it over L.A.

I feel the complete ET flight report will assign some contributing factor to the crew for not slowing down, and likely mention CRM. I feel that they did not know enough about the mechanization of MCAS that kept applying nose down trim when they were not countering it with the button of the wheel, plus the 5 second delay, plus......

Gums opines...
Hi Gums,

Sorry for the late reply- busy week and a hockey tournament for kids so hadn't checked in for awhile.

It's a great question to ask, both to illuminate why this was not a possible out for either of the crews, and also realistically how real unusual attitude training and experience (as opposed to the lip service now given) could save lives.

First some clarification of definitions. The terms aileron roll and barrel roll have been variously conflated and misdescribed by numerous posters. I'm not going to revisit the descriptions, just describe each accurately here. An aileron roll is a roll performed in level flight, around the center horizontal axis of the airplane. It is an uncoordinated roll, meaning that all three primary controls are used individually to perform the maneuver. You start the roll by applying full left aileron (in western powered aircraft anyway) and as the airplane rolls through 45 towards 90 degrees you feed in right (top) rudder to keep the nose above the horizon. As you pass 90 degrees you start rolling out the rudder and adding nose down stick, again to keep the nose above the horizon. Rudder goes to neutral at the 180 degree point and maximum (necessary) forward stick is reached. As you roll towards 270 degrees forward stick is relaxed while left (top) rudder is added until at 270 degrees the elevator is neutral, left rudder is at it's max, which you begin to remove as you roll back towards positive 1G flight. I should properly note (ironically) that usually you set the trim to aerobatic neutral, which will require significant back pressure in level upright flight and less forward pressure when negative, so some of the timings I listed above would in reality be off a bit. Finally- you will go through a full range of +1 to -1 to +1G through the maneuver.

A barrel roll Is a roll begun from level flight and it is a fully coordinated roll. In an appropriately powered airplane you can start from straight and level, but for most you want to enter a shallow dive up to Vmc or so before beginning a smooth slightly more than 1G pullup to bring the nose anywhere from 30 to perhaps 50 degrees above the horizon if you have a really slow roll rate. If you do this properly you have placed the airplane on a ballistic trajectory which will allow you plenty of time to roll through 360 degrees before returning to your start altitude. Once you have a positive rate of climb you begin to roll in coordinated form (Aileron and rudder) until you pass through the inverted position hopefully a little before you reach the top of your climb. (This allows you to control exit altitude safely.) Throughout this rolling sequence the airplane will be changing heading- first to the left, and after rolling inverted back eventually to the original heading. This isn't really a 1G maneuver as you cannot get the airplane nose up, or recover from the nose down finish at 1G, but it is very benign and properly performed need not be more than 1.5-2G.

A bunt is a nose down pitching maneuver that ends up as 1/2 or a full loop. Historically a bunt is begun from level flight, by retarding power and when your target airspeed is hit and you have confirmed enough altitude for safety you begin to smoothly feed in nose down stick, increasing the amount of stick as you approach inverted due to the increased airspeed and need to maintain a constant radius. To do this your angular velocity must increase, hence the need to push harder. This is one of the most abstractly terrifying maneuvers anyone can do and it is distinctly uncomfortable as at maxim rate of change/g loading you will be pushing between 5 and 6.5G at a minimum.

Hopefully from that you will see that what is being discussed here is a possible combination of two figures- the barrel roll and the bunt.

I have to go get kids, so let's call that Part I and I'll try to finish tonight.

wonkazoo is offline