Questions for 737 pilots

[mjc507]

I have several questions for the men and women who fly the B737. I spend a lot of time flying on the Microsoft Flight Simulator and the more involved I get the more interested I am in flying for real some day.

First, I hope someone can help me to understand how the stab trim is calculated. I know it has to do with the weight of the aircraft, but I am looking for a formula that is generally used.

Second, can you tell me how the SID/STARs are chosen? What I mean is are you able to determine which departure/approach you want or is this information given within your ACARS? I have noticed that some of the SIDs I fly (on the simulator) out of EGLL or EGKK seem to have you flying at low altitudes for over 30nms only to turn you around on a 180 where you may climb to TA060 (which may only be 2000 ft abv where you've just been). Is this not wasting valuable fuel or are you able to delete some of those waypoints?

Third, I may have read that when setting the decision height you add 200 feet to the airport altitude. So if EGLL has an altitude of 80 feet am I to set 280 in the DH? If this is true then how would you set the DH for a city like Denver where the altitude is over 1,000 feet as there are only three numbers in the DH window?

Finally, I know there is some debate about when anti-ice should be used. Could you give me a general rule of thumb of when to use it both on the ground and in flight? Is it true that if the anti-ice is used in flight the start switches must remain in CONT. mode?

I appreciate any help that can be provided to me as I am very interested in someday flying the real thing for myself.
Cheers,

Michael

[NoseGear]

Hi Micheal,

A few answers for you:

1) You're right, Stab Trim is calculated on A/C weight, and is based on % of Mean Aerodynamic Chord to A/C C of G. To calculate it you take the A/C weight, look on a chart in the A/C and it will give you Stab Trim settings for Takeoff. I am unaware of a calculation that you can do without a chart. On the Stab Trim indicator there is a green band that the Stab Trim must be in for Takeoff, if it is not, you will hear a warning horn sound when you advance the thrust levers. The Takeoff range is around 2.5 to 10 units, but as a general rule, you can use 4.5 to 5 units for midweights.

2) As for SID's, they are assigned by ATC, and input using the FMC. You have to fly the SID you are given. I don't fly in the UK, but there is a great deal of traffic there, so the entire SIDs are generally flown to keep you clear of arriving traffic and other departures and to assist with flow control. Usually, the SID is assigned depending on where you are heading. ACARS is generally used for company messages. You can only delete the waypoints if ATC clears you to "Canel SID, cleared direct to...."

STARS are for the same thing, flow control for arrivals, and again, you are assigned a STAR depending on the direction you are arriving from. If you can get a chart, you will see several arrivals for each runway.

3) As for adding 200 feet to DH, perhaps you're thinking of the pressurization system, which is set 200 feet below departure airfeild elevation.

4) Engine Anti-ice: Must be ON during all ground and flight operations when Icing Condx exist or are anticipated, except during climb and cruise when the Temp is below -40C. Must be ON prior to, and during descent in all Icing Condx including temps below -40C.

Icing Condx are considered present when the Temp is below 10C and visible moisture is present, ie. rain, snow, sleet or cloud.

Start switches are ON during icing condx. to prevent possible flameout.

As for Takeoff, leave the Wing Anti-ice on as it will automatically trip off at liftoff.

I hope that answers some of your questions, and believe me, the real thing is far, far better than the sims, so get going, you will never regret it. I'm sure all 737 drivers out there would agree.

Nosey:ok:

[Bokomoko]

1. The takeoff stab trim position is adjusted based on airplane center of gravity (C.G.) and takeoff flaps for a determined situation. For a B737-300 - if cargo, fuel and passenger are properly distributed - takeoff stab trim settings are from 1.0 to 6.3 units. Higher settings mean heavier on forward area and opposite for lower stab trim units. Additionally - to prevent a takeoff maneuver using a stab trim setting out of maximum limits – there are two more alerts to the pilots: a display of a green band on stab trim pointing out the maximum takeoff setting range and a horn will sound if throttles are advanced, during takeoff with the stab trim beyond that green band (one of the conditions for the takeoff configuration warning).

2. In congested terminal areas - and mainly those with many adjacent airports - there are standard procedures to organize the traffic flow. SIDs and STARs are prepared and used to facilitate controller and pilot works when airplanes are leaving or arriving those airspaces. They’re based on pre-arranged tracks and altitudes. When crossing routes or corridors are not used for a period of time or if there’s a low traffic demand in a determined area, procedures can be abbreviated. Normally, there’s a standard route for inbound/outbound traffic to a specific sector or area and under normal operation pilots can’t choose if they want (or not) to fly them except if traffic permits. Fuel on board is adjusted considering those situations.

3. It depends. Decision Height (DH) is normally set during precision approaches and there isn’t a fixed 200-ft setting. That value must be checked for every airport and procedure in use (for example, during an approach based on ILS category I or II or for a same runway but different threshold). However, that setting is a reference to the pilots and airplane systems and it considers the airplane vertical distance to the ground, for a determined point during approach. When you adjust 280ft on Radio Altimeter dial that means the alert will be displayed when the airplane is 280ft above the ground.

4. Engine A/I must be on during all ground and flight operations when icing
conditions exist or are anticipated, except during climb and cruise when the
temperature is below –40 C SAT. Engine A/I must be on prior to, and during,
descent in all icing conditions, including temperatures below –40 C SAT. For wing A/I ground operation uses the same procedure for engine A/I. In flight there’re 2 methods: de-icer (allowing ice to accumulate before turning on the system) and anti-ice (prior to ice accumulation - procedure used only during extended operations into moderate or severe icing conditions). CFM engines used on B737-3/4/5/6/7/800 require the engine start switches in CONT. As far I remember engine used on B737-200 (PW JT8) when engine A/I system is turned on and after engine EPR is stabilized engine start switches can be off.

[mjc507]

I appreciate your answers and, yes, I do hope to fly the real thing one day. Can I ask perhaps a stupid question relating to the anti-ice? Is the engine anti-ice used during cruise? For example, I also like to fly the 767-300ER from London to East coast US on the simulator. I use real world weather and will fly at FL380. I will often have OAT of -50C. Would the anti-ice be turned on even though the weather around me is not severe (i.e. no snow storms in the area below)? Also, is the wing anti-ice used in cruise or just before descent since they have been exposed to pretty cold air?

So the DH is not related to the airport elevation. If I were looking at an ILS chart where would I find the info for the DH?

Can you handle one more question? I understand now how the SID/STARS are determined in relation to the flight routing. Here is my example. I have departed EGLL for KBWI. My first waypoint on my route is SFD(Seaford). My SID is a SFD8P and reads thus: Climb straight ahead to I-GG until 3 DME then turn right to SFD21 where I need to be at or above 2000ft. Then I fly right to SFD17 (which is 30nm away) where I need to be at or above 3000 feet. Then a complete 180 and another 30nms or so to SFD14 where I need to be at or above 4000ft. Then, another 180(!) to SFD7 where I need to be at TA060. Finally back 180 to Seaford transition to join my flight plan. I don't understand why I couldn't just fly to my transition altitude in the first place (which would have happened long before I hit Seaford VOR) and thence to my plan. I do understand the aircraft separation need but is this simply wasteful of fuel? Perhaps the SIDS/STARS of the US are not so erratic?

Anyway, many thanks for your kind explanations.

Cheers,

Michael

[NoseGear]

Hi again Micheal, glad to help. For some good info re: Anti-ice see Bokomoko's post, he explains it well.

The thing to remember with using Anti-ice is that the supply of hot air comes from bleed air drawn from the engines. When you have anti-ice on, there is a greater requirement for bleed air. The way the engine corrects for this increase in demand is to increase thrust to allow for the increased bleed air demand. If you leave anti-ice on when not required you get an increase in fuel burn, which is not a favourable condition. As for the 767 (I don't fly a 767) the only reason you would use anti-ice in the cruise would be if you encountered "visible moisture". At FL380 over the Atlantic, at -50C, and no storms around as you said, there would be no need for it. There is no requirement to heat the wings for or during descent, unless descending into icing conditions.

If you are looking for the DH on a Jepp chart you need to look at the bottom of the approach plate, and you will see an area with boxed information, there you will see something like this:
DA(H) 222' (200')
That is your Decision Altitude (Height), which is for a CAT 1 ILS. The difference between the 2 heights above is the DA takes into account the airport elevation. But the DA is the height at which you commence the missed approach.

As for the SID you described, it sounds pretty painful, and as I don't have the charts, I really can't say. It may be for terrain clearance as you seem to crossing the Seaford VOR 3 times, back and forth. Or perhaps for noise abatement in the area. As for the transition altitude this is for providing flight levels above this altitude and below is on area QNH. As far as going direct to your transition altitude this would be irrelevant. In normal operations, you would probably be cleared higher during the SID, but again, that depends on traffic. The altitudes you mention in the SID are minimum heights you must obtain, not maximum. In real world ops, you would probably be cleared higher, and possible once above your MSA, cleared direct to next waypoint. Check for the MSA, Minimum Safe Altitude and see what it is. It is more important than transition altitude.

Hope this helps, perhaps someone who flys in the region can shed some more light on it. I would highly recommend going down to your local aeroclub and talking with one of the instructors, taking some lessons and seeing how much more fun it is doing it in the real world yourself.

Good luck

Nosey
PS. I don't fly in the US either, keep guessing!
:ok:

[onehunga]

Michael,

I don't think you have a correct SID for LHR. Try the weblink below:

http://www.ais.org.uk/aes/pubs/aip/html/egll.htm

[mjc507]

I appreciate everyone's response to my questions. I am very interested in commercial aviation and I enjoy hearing from all of you who do this for real. Thanks to Bokomoko and Nosegear for clearing up the anti-ice questions for me and thank you Onehunga for the web link. This will be a great help.

Since everyone has been so helpful I hope you won't mind a few more questions that I have.

1. What is the difference between a CAT II ILS approach and a CAT III ILS approach and which does the 737 use?

2. During an ILS landing on the flight simulator (Microsoft's, that is) I press the VOR/LOC as I turn towards the localizer and then adjust my Vspeeds and flaps as required. Once the glideslope becomes active I press the APP switch and the command B autopilot so that both autopilots are engaged. The problem I am having is that once I capture the glide slope the plane takes a gut-wrenching dip and often falls below the glideslope with a GPWS warning about "glideslope". Sometimes the speed will stabilise the aircraft and sometimes it won't. Do you encounter the same activity when the real bird captures the glideslope? Should I press the APP switch later than I do? Any help and/or description of what you do for real would be greatly appreciated.

3. What procedure(s) do you do before your T/D to make the 737 descend to its first altitude while engaged in VNAV? What I mean is on the descent page of the FMS there is a line select item called "capture". When is this used (or if at all)? I often press the "capture" about 10nm from the T/D and then change the altitude in the MCP. Sometimes the plane will descend on its own and sometimes I will pass the T/D and will have to press the VNAV switch again to engage. What is the correct procedure?

That's it for now. I hope I'm not overstaying my welcome with all of you. I am very aware that I am simply a "wannabe" but I still have the flying bug, whether real or simulated.

Cheers,

Michael

[Bokomoko]

First, my apologizes to nosegear, next time I’ll refresh my computer prior to leave my message. You answered the questions very well.

MJC
1. Differences between ILS cat II and III are basically airport, aircraft, operator and crew certifications and weather minimums. Based on ICAO standards, Cat II is an ILS approach procedure which provides for an approach to a decision height lower than 200ft but not lower than 100ft and RVR not less than 350m. Cat III are divided in 3 categories: IIIA – with a DH lower than 100ft or without a DH and with a runway visual range of not less than 200m, IIIB a decision height lower than 50ft or without a DH not less than 50m and IIIC with no DH and no RVR limitations. Which does the 737 use? Well, it depends on what certification the operator has. B737EFIS and NGs are certified to ILS cat IIIA.

2. Usually, under normal operation there’s no such condition you described. Your procedure to engage the second A/P is operational (maybe there’re some SOP differences among certain carriers), but tell me: First, were both nav receivers tuned to the same ILS frequency? Second, was the same inbound ILS course set on both HSIs? Have you been flying with flaps 5 and speed no faster than 170-180kt prior to intercept the GS?

3. When using VNAV, and no early descent is required pilots just have to set the altitude, using altitude control knob on the FCP. The “Capture” function is used during an early initiation of path or speed descent. VNAV path descent is at 1000 fpm until intercepting the computed path.

Nice flights

[mjc507]

Thanks very much for all the info. This is really very helpful to me. I don't mind that you didn't see Nosegears post when you responded. It shows that you both have the same info to relate instead of two very different answers which would have confused me to no end.

The ILS approach I was talking about was based on a "checklist" that a fellow simmer had written up. As it doesn't always work well I figured that I was either doing something wrong or there was simply a bug in the program.

To clarify: both of my nav radios were tuned to the localizer frequency an in the manual mode. The inbound course was also set on both HSIs (say 273 for EGLL RW27R). The Vspeeds were as thus, because of my weight the flap 15 speed was at 148 and flap 30 was 132. I slowed to 190 for flaps one and 180 for flaps 5 once my VOR/LOC was captured. At that point it was speed 170 for flaps 10. According to my "checklist" just before glideslope capture I would set speed for flaps 15 and once the glideslope was active vref+5 for a flap 30 landing.

This topic has been a big issue with my fellow simmers so enough chit chat from them I want to hear it from the non-virtual pilot. I also have a very nice video of a GO flight from Stanstead to Lisbon that shows the entire flight and when the F/O talks about the possiblity of a missed approach he does mention that both autopilots are engaged for an autoland. This may be their airline procedure, though.

Also at about 6 miles from the RW the captain turned off the speed and disconnected the autopilot.

As far as the descent issue is concerned, I have placed my descent altitude in the MCP to the first leg of my STAR but the plane stays at cruise until I intervene. This may simply be a glitch in the program.

I look forward to hearing your side of the story on all this. My fellow "wannabes" mean well and are ofen helpful but they aren't sitting where you are.

Cheers,

Michael

[csfpm560]

with reference to your comment of "keep guessing"
I would guess that you havent got a flying job yet.
Am I correct?

[SpamCanDriver]

I have the Go video aswell so I know what your talking about. Although im not a 737 pilot yet (start type rating Jan) I think I can answer your question about autopliots on autolands. On a 2 autopilot plane like the 737 both autopliots are engaged for an autoland. This is so if one fails during the approach there is still something flying the plane. However if an autopilot fails during the approach above DA a missed approach would be executed as you must have at least two functioning autopilots to execute an autoland. But on plane with 3 autopilots 747 400 for example its the at the commanders discretions to continue the apprch if one of the autopilots pops out above DA, as they still have two functioning autopilots. These two different systems are known as fail-passive and fail-operational respectively.
As for why the Captian disengages the autopilot and Autothrottle at 6 miles in the video, this is because he is visual with the rwy and able to carry out an manual landing, which contrary to popular belief we will do whenever possible. Why let the autopilot have all the fun!!:{
Hope this helps

[Flight Detent]

Hi all,
Just a little addition to the aforementioned B737 anti/deicing system useage.
In the NG series, I believe the comments earlier are correct in that the wing anti-ice switch does click off on liftoff, but the bleed air supply has already been shutoff as the power levers were advanced for takeoff.
Further, if the WAI is selected anytime inflight, the stickshaker setting is altered for the remainder of the flight, regardless of whether WAI is subsequently turned off.

Cheers ;)