Advice on how to be stable by 1000 feet. What NOT to do?

[WhySoTough]

Surely me, and many other newbies can benefit from advice from the more experienced.
My company has a policy of being stable by 1000 feet.
Speed +10/-5 from Vapp/GS mini, of course in landing config.

Now I'm looking for ways to stay out of trouble. Things to avoid, any tips, etc.
Does ATC often leave you high and mess up your approach?
I believe if you intercept GS from above, your speed would be high, ROD too high, etc, that could maybe lead to being unstable. (correct me if I'm wrong please).
Also, I've read sometimes if you've messed up the approach, you will be on final at thrust idle, surely that's a go around if you're at 1000 feet, but how would one get into this situation?

Can a tailwind cause an unstable approach in terms of keeping you high on speed, or will ground speed mini take care of this? With gusty winds and the speed fluctuating a it, I assume that is usually normal?

I'm just looking for some advice from guys that have a lot more experience.
Will appreciate your responses.

Thanks!

[Airmann]

From what I've heard/been taught:

Work your descent backwards, using the formula: 300 feet for every mile to go.

e.g. 10 miles 3000 feet.
38 miles 11,400 feet and so on.

(Some people say 1000 ft for every 3 miles, but the above is more conservative, I personally prefer it but its up to you)

Make sure the flight plan is properly sequenced so that you know the track miles to go, don't just look at the direct distance.
Keep checking the Prog page for your Vdev, if in doubt stay below it. Only works if flight plan is sequenced.
If you need to be stable at 1000 feet plan to be stable by 1500.
Remember on the 320, if that's what you fly, and you might since you're talking about GSmini, you can bleed off 10kts/mile without spoilers and 20kts/mile with.
If you ask around people will give you tips on which config to put the aircraft to get the best descent angle. If you're capturing the glide from above its probably better to be slow and fully configured rather than being fast and unconfigured.

Those are my tips. There are a lot more experienced guys here who can probably give you some great advice

[Green Guard]

Good thing today is you can always see your ground speed, your actual wind and actual distance to Threshold....

It happens sometimes to have near calm wind on runway and up to or more then 50 kts tailwind on just above 1000' AFE. Either change RWY or read no.2 again.

1. Always check the wind. And always know where you are by hight vs distance. For example 3 x (ALT- Elev)/1000 =Dist in NM where you should be on 3 deg GS.( or disregard those zeroes and just use thousands of (ALT - Elev) x 3). Electronic GS will not show u where u are, if you are much left/right or more then 2 dots above, or further then 18 (25 NM) or so..
2. You must accept ATC to bring you here or there, but you need to be ready to adjust yourself. If you are high, first do something against the logic, LEVEL OFF, extend flaps and /or LG as necessary, so even if u come from above GS you are in control, and easily STABLE at 1000' AFE

;)

[Intruder]

Follow your company policy -- ALWAYS. If conflict between policy and ATC restrictions cause a go-around, so be it.

However, you often have to be proactive to be able to abide by EXPECTED restrictions, such as "160 knots to 4 DME." Configure early so that at 4 DME you can IMMEDIATELY reduce to final approach speed. If you need to carry more thrust to 4 DME, so be it. Vocalize your plan to the other pilot as you make the decisions. CALL FOR the flaps/gear as you want them -- don't ask. He'll likely suggest something else if he doesn't like it.

If you are too high and/or fast above 2000' MSL, do not be afraid to use all the drag devices on the airplane -- including the landing gear. If your manuals say use of speedbrakes with flaps is "not recommended" (but not prohibited) use them as needed, but let the PM know what you're doing (e.g., "Nonstandard; speedbrakes coming out until 2000'.").

VNAV will NOT intercept the GS from above in most airplanes, so use V/S and whatever rate of descent you need. Fly it manually and have the PM set up the MCP as if the autopilot were engaged, so you have the Flight Director as baseline guidance. Then FLY THE AIRPLANE to make it do what you want.

[Uplinker]

Half the battle is your descent planning.

Keep in mind that 3 x your required height change in thousands of feet will be the track miles you need to descend, and 5 x your groundspeed is the rate of descent you need. So if you are at 35,000 feet with a ground speed of 360 knots, you will need 105 miles at 1,800 ft/min. Remember though, you will need an extra 5-10 miles to slow down too. Keep an eye on the wind on the way down, because obviously it can change, requiring a different rate of descent.

Put in F speed and the ILS platform height as a constraint in the flight plan at the point where you expect to capture the glide, and put in the descent winds all the way down. The aircraft will work everything out (but mentally cross check it as above), and will give you a realistic top of descent point at which to request descent from ATC. This will mean that you will be in the right ballpark on initial approach in terms of energy control without having to grab handfuls of speed brake, or even the gear, to slow down and go down. Of course, the actual descent profile will be largely what ATC give you, and they may still ask you to 'slow down and go down', but if you've asked for descent in good time, and got the speed under control, you will be better placed to accommodate ATC.

The key to a stablised approach is speed and energy control. If you come screaming down the ILS, your engines will be at idle at 1,000, because you will still be trying to slow down - this could lead to an unstable approach and you will have to go around. Aim to take 'flap1', (i.e. the slats), at around 15 track miles out until you get comfortable with the energy management.

A tailwind can cause an unstable approach, and if the tailwind is too much, too low down and you're not stable at 1,000'; a go around, followed by vectors to an alternative runway will have to be used - but that won't be your fault.

Hint: If you can't do 5 x groundspeed in your head easily; simply halve your groundspeed and add a zero - it gives the same answer, e.g. G/S = 430 kts, V/S required is 2,150 ft/min.

[Robert G Mugabe]

If in doubt take the gear early.

[PENKO]

There is always the gear.
Honestly, there is almost no excuse for not being stable at 1000.
Tailwind? It's a gotcha but if you are alert and configure early, no problem at all.
Short cuts? Use the gear if too high. Rarely do you end up so high after a shortcut that lowering the gear early is not enough. Rarely. And when it does happen (i.e. you have been asleep during the approach and did not see it coming) you just decline the shortcut.

Anyway, this all means nothing if you have not got the experience yet. And once you have the experience, it will sound like teaching your grandmother to suck eggs...

Don't worry too much about it, it's not rocket science. Just look to the left for now. When the captain starts shifting in his seat, you'll know you are coming in hot.

[tubby linton]

The effect of the gear is maximised whilst it is in transit and the doors are opening. Once the gear is fully down and the doors closed the drag effect lessens but is still better than a clean aircraft.
In the good old days when we all used to fly decel approaches the cut off was flap 1 at S speed by 2000ft aal at the latest, but obviously not in imc.

[WhySoTough]

Thank you guys very much for the advice.
I personally find alt to lose x 3 easier than multiplying track miles.
Anyway, how exactly do I know what to expect though. The FMS has the STAR and the full procedure for the ILS, surely it's adding alot of track miles. I'm not sure where the ATC will cut me off and give me headings, etc.

One of the TRIs told me in my stage he'd rather me be low and slow, so basically TRY to maintain a constant 3 degree glide path, but if I'm confused, just descend down and make sure to be lower, rather than higher..
I've only recently started line training and remember the captain looking at me like I'm some kind of retard when I asked for flap 1 at 13 miles for an ILS app. :ugh:
I like to intercept the LOC at a slower speed, keep the workload less by first configuring, than being stable, etc.

Unlinker, didnt see anyone doing the F speed and platform alt constraint, but definitely a good idea!

Finally one more ques. Does ATC leave you high, to capture from above very often?
In this case, if fully configured and selecting VS - 1500, the aircraft pitches down to match that VS. Autothrust will do its best to maintain speed, but The VS is the priority. Can i be sure autothrust won't be on idle because I'm fully configured?
Sorry, I've performed this only once in the sim very briefly, still confuses me.


Thanks all for the informative posts. Appreciate the help!

[compressor stall]

Remember though that slowing up too early will leave you high... If you need to loose height without the spoilers, keep the speed on.

[sevenstrokeroll]

assuming you are flying to the same airports over and over, you can get a clue as to likelyhood of tailwinds in descent, atc habits and the like. IF you are X from the runway and you are too high, say: ATC WE WANT LOWER NOW. control the situation.

for example, going into Boston, runway 4l/r, there is always a tailwind aloft and a headwind at low altitude. an old guy should tell the new guy about this...but if not, you will learn and be nicer to the next guy and tell him so he can be ready.

all you high tech plane guys have groundspeed, wind readout and the like. you shouldn't be caught high or fast...but again, tell ATC what you want, not what they want to give you.

[Intruder]

Finally one more ques. Does ATC leave you high, to capture from above very often?
In this case, if fully configured and selecting VS - 1500, the aircraft pitches down to match that VS. Autothrust will do its best to maintain speed, but The VS is the priority. Can i be sure autothrust won't be on idle because I'm fully configured?
Sorry, I've performed this only once in the sim very briefly, still confuses me.
They don't do it routinely in most places, but it happens all too often...

Autothrust will use any setting between idle and Ref to attempt to maintain V/S. Once thrust is at the limit, airspeed will be sacrificed to STILL maintain V/S.

You haven't told us your airplane type, but with landing flaps the idle thrust will likely be approach idle, not flight idle. With landing flaps, you should be able to maintain a reasonable approach speed range at -1500 fpm. However, when intercepting the G/S from above, 2500 fpm or more (above 2000') may be required to get on G/S and stable by 1000' / 3 miles...

[WhySoTough]

Thanks once again guys.
Intruder, my apologies I forgot to mention it is the a320.
I am pretty sure I remember my captain on that session saying 1500-2000 fpm, but not more than 2000fpm.. SOP doesn't say anything specific.. Just to set FCU alt above current alt, and to use VS mode..

[cactusbusdrvr]

We are often hot and high in the US, ATC likes to jam us in when they can. We are usually expected to maintain 170 to 180 knts to a 5 mile final, which is 1500' AGL (coincides with the 300' per mile formula). So we are rarely Vapp plus 10 at the 1000' gate. And it really does not matter. If you are stable on the glide slope but fast you will in almost all cases be stable by 500'. We have a hard gate at 500' and a soft gate (must be stable at 1000' in IMC) at 1000'. Fully configured at 1000' will get you on speed at 500', I say that because you can't go flaps full over 177 kts (flaps 3 at 185). So you would be in a reasonable speed range to slow to Vapp inside of 1000'.

I use speedbrake and flaps 2 to get down. If I am unstable I turn the autopilot off and just drive it on down to capture the glideslope, open descent down to FAF altitude. If I am really high I will drop the gear, that's a lot of drag with the boards out and flaps 2.

One last thing, if you are at 210 kts (a usual ATC speed here) and given a descent don't be in a hurry to o flaps 1. Once those slats come out then you go to approach idle which gives you an extra 400# fuel flow per side, which you generally don't want if you are trying to get down.

All this is for a 320. For a 319 you have to configure 1 mile sooner.

[The African Dude]

As you mentioned G/S intercept from above, we use a simlar procedure:
Wind FCU Alt up to force V/S mode
V/S -1500
Gear Down
Flap 2

Re. knowing where to expect shortcuts and the like, you can bring TCAS in to your scan. Scan for traffic ahead of you in the approach sequence, listen to what ATC are telling them and build a picture of what they might ask from you in the near future. And if you need more track mileage do ask for it. The G/S intercept from above should be a last resort.

And FWIW Flap 1 at 13 miles is perfectly normal. Unfortunately thee are many guys out there who complain that you're wasting their share options by using speedbrake or getting down in good time. My advice is to not let those attitudes get to you or affect your judgement of what is sensible in the situation.

[A4]

I think Uplinkers post pretty much summarises it!

In the early days of your training BE CONSERVATIVE - don't try to be "slick". F1 at 13D is perfectly acceptable and shame on the Trainer if he gave you a disparaging look.

One common error I have seen is people putting MORE energy into an approach when high i.e. increasing speed to dive off height. This is ok but it depends where you are in the approach. If you're at 30D you still have time to bleed the speed off but 15D or less - SLOW DOWN and configure. More energy=less time=higher workload=mistakes/unstable.

The 3 x table is a good back up for a correctly programmed/sequenced FMGC. Again, early days, use 3 x your height + 10 miles. The PROG PAGE profile deviation is ONLY AS GOOD AS THE INFO IT'S WORKING WITH! assuming you're not on a P-RNAV arrival and your not going to bust any altitude restrictions then "tell" the aircraft what you would like it to be doing at a certain point. For example, if there's a waypoint on about a 15 mile base leg in the arrival you could put a constraint of 210 knots/4000'(agl). The aircraft will now work to this constraint and tell you if your hi/lo on your target allowing you to intervene as appropriate. (There is a "gotcha" with profile information sometimes - long story short just perform a DIR TO your next waypoint (and pull HDG again if in HDG!) to force a recompute of the profile.

Another big help is the wind arrow on the ND - think what that's doing to your ground speed and how it may affect you on base/final. If you're unsure what ATC are going to give you in terms of track miles - ask them! They are a service and there to help (with some exceptions :rolleyes: ). Additionally seeing how the aircraft ahead are being vectored using your TCAS can give heads up to probable routing.

Finally, at this stage, I recommend you get F2 out prior to GS*. The A320 tends to "balloon" when F2 is selected which then makes trying to slow and maintain the glideslope a little more difficult - particularly with tailwind or no headwind. Additionally F2 gives you some Flap (drag) whereas F1 is slat only so not much use other than getting you below 200 knots to allow F2.

There's a lot of good advice in all the posts on this thread. Keep thinking ahead of the aircraft, use all resources to enhance your overall situational awareness and be cautious. As your experience and confidence increase you will start to fly to less conservative parameters but still be able to maintain safety meeting all stability requirements. This is your goal but don't rush to achieve it - it will take time.

Enjoy!!

A4

cactusbusdrvr said:

I use speedbrake and flaps 2 to get down. If I am unstable I turn the autopilot off and just drive it on down to capture the glideslope, open descent down to FAF altitude. If I am really high I will drop the gear, that's a lot of drag with the boards out and flaps 2.

I'd caution this for a new Trainee. You can achieve VERY HIGH rates of descent with OP DES+F2+Speedbrake - MASSIVE with gear too. You would have to be really really high to require all this to achieve profile and it would probably be due to a an ATC screw up or you not being proactive earlier on in the approach. OP DES towards glide slope is also not a great idea because you will be at THR IDLE. GS from above procedure requires use of V/S 1500'/min because it keeps the A/THR in SPEED mode. High drag, thrust idle, "diving" from above is not how airliners should be flown. If it's got to that stage then perhaps it's time to throw it away and have another go. Additionally, in such a high workload scenario, think about the consequences of forgetting to arm the APPR.......

Fly safe.

4

[Ollie Onion]

The most frustrating thing I see almost daily is pilots / trainees trying to 'thread the needle' and be stable AT the required altitude instead of being conservative and giving a bit of room for error. If my hard stable limit was 1000' then I would aim to be stable by 1500'. If you are you can enjoy the scenery, if you slightly miss it then no matter. The ones who get themselves in trouble are those who consider it some sort of personal failure if flap full doesn't hit the stops at 1000'.

Personally I find that the A320 is easy with Flap 1 'S' speed on LOC intercept and Flap 2 and decelerating to 160 kts by the G/S intercept. At 2000 RA the gear goes down and flap 3 and full once gear down. 99% go the time this will have you stable at 1,500'.

[FullWings]

I think it's down to motivation. How many unstable approaches would there be if each pilot was docked £500 for busting SAC and not going round? Money could go to an aviation related charity... :)

The problem's not that hard, compared with other things we have to contend with. Work out your minimum track miles, know your three times table, be aware how speed/distance trade in your aircraft and... errmm... that's about it.

[Uplinker]

Definitely be conservative.

Shame on the "trainer" who gave you a bad time for asking for flap 1 at 13 miles! Probably one of the small-willy brigade who try to pretend they are somehow better or cleverer human beings than a brand new trainee. Ignore them - I used to get it myself - a long pause after me asking and them reluctantly selecting the lever. But on their own leg; they get a bit hot and high and they were a mess - speed brakes in and out - grabbing flaps at Vfe and intercepting the glide from above etc. These are the sort of people who get to 1,000' with the speed brake still out and have to go around.

Regarding the F speed constraint; if the kit will help you, why not use it?

(By the way: Yes, you can do 200 knots to 4 miles - just - (in a BAe146), if you have lots of experience, but that's not how we do it anymore, and nor should we).

To answer your question about what to expect, I'm afraid that really is part of having experience of the airports, which of course you don't have yet. Before you brief the approach, ask the Captain if ATC tend to keep you hot and high, and know what to do if they do - (get low and slow as early as possible). Know how to intercept the Glide from above - understand that SPEED ALT* will block glideslope capture if it coincides. (Hint: use V/S to descend at 500-200ft/min to intercept the glideslope before reaching the selected ALT). Remember, as many others have said: if you need more drag, the gear can be taken early, out of the normal flap sequence - just say "non-standard - gear down please" so the other guy understands what you're doing.


U

[WhySoTough]

Uplinker,

Thanks once again for the response. Just a few things I didnt quiet understand.

"understand that SPEED ALT* will block glideslope capture if it coincides. (Hint: use V/S to descend at 500-200ft/min to intercept the glideslope before reaching the selected ALT"

What exactly do you mean the speed ALT* will block GS capt if it coincides.
Can you explain a scenario how that will happen?
Also, using 500-200 to intercept when for example ATC has cleared me to descend to 2000(platform alt for example), and cleared for the ILS, when I'm 9 miles out and not very high above the 2000 alt already?

Just a little confused with this.
Thanks once again mate.

[A4]

WST.

Picture the scene, you're cleared to descend to 2000' and "further with the glide" but you're already above the glideslope. You set 2000' and select V/S -1500 FPM but just when you're at "half dot high" on glide the FMA annuciates ALT*. This is because you have a high rate of descent and the autoflight system anticipates the level off...... so the aircraft starts to level and increase thrust :eek:

The correct method to avoid this is to set the altitude above your current altitude BUT YOU MUST ARM THE APPR!!!!!!!! IF YOU DONT YOU HAVE NOTHING TO STOP YOU DRIVING INTO THE GROUND.

So GS from above is:

1. Configure - drag to combat the increased rate of descent - Gear + F2 works.
2. Set the altitude above your current.
3. V/S -1500' FPM (2000'FPM is ok further out on the approach)
4.ARM THE APPROACH so you don't fly through the glideslope.

If it isn't going to work...... go-around..... don't try and make it work.

A4

[Icelanta]

The most important thing in the cockpit is common sense. if the engines are starting to spool up or when the speed is still a bit high but configured, no need at all to go around. Common sense has priority over blind slave of the procedure. this is not to say that you should not aim for a completely stabilised aircraft according your SOP.

[Uplinker]

Hi WhySoTough.

Often you will get the scenario where you are LOC established, say at 3,000', all fine and good. However, then ATC realises that they've left you a bit high or a bit close, and so give you clearance to "descend 2,500' and further with the glide".

So you dial in 2,500' and pull to descend, and also arm the glideslope. You now have G/S and ALT modes both armed in blue. But, as you watch the glideslope lozenge coming down towards the altitude lubber line, the 2,500 blue alt box also comes up towards the same lubber line. Sod's law says that the aircraft will get down to the cleared altitude before the glideslope and go into ALT*. While it is doing this, it will ignore the glideslope completely and you will fly level, past the glideslope intercept point, leaving you above the glide!

The way around this, if you see it coming, is to select and pull a V/S range between say -500 and -200, so that you descend more slowly, and will therefore reach the glideslope before the selected altitude. Then the aircraft will capture the glide, go into GLIDE* and ignore the altitude. This is a good time for you to set the missed approach alt.

I hope that makes sense? - It's much easier to do than explain!




U

[cactusbusdrvr]

AA, good point about the open descent scenario I talked about. That is why I specified only to FAF altitude and yes, you would have to arm the APP button.

We have a lot of slam dunks in the US. The approach into SNA is typical of what I am speaking of. You are coming in over the Coast mountains about 15 miles from the runway. The MVA is 5700' for a sea levelish (50') airport. If you get the left base entry to the localizer you have to lose 3500 feet in about 8 or 9 miles. That's the scenario I was asking about.or our approach into PANC at night. Over the Chugash mountains at 8000 feet, descending over the water abeam the airport at 6000', cleared the approach. You have to dump it down with flaps 2 and speed brakes, the gear if you keep 250kts until base. It becomes a challenge to manage the energy properly, a challenge that makes the job a lot more than "just driving the bus".

As for getting on the trainee for flaps 1 at 13 miles? Utter stupidity. Unless you are number one with no one else around I would expect that ATC wants you at 180 to 210 kts. That's calling for flaps 1.

Be conservative but also be willing to push your comfort level. The idea is to minimize drag and keep fuel flow to a minimum until you must be spooled and stable, be it at 1000' AGL or 500' AGL. Hopefully you as a new guy will have an experienced check airman that will be competent enough to let you work this out for yourself.

Remember,a experienced pilot is just someone who screwed up but lived to learn the lesson. (tongue in cheek there for the humor challenged).

[A4]

Uplinker said:

So you dial in 2,500' and pull to descend, and also arm the glideslope. You now have G/S and ALT modes both armed in blue. But, as you watch the glideslope lozenge coming down towards the altitude lubber line, the 2,500 blue alt box also comes up towards the same lubber line. Sod's law says that the aircraft will get down to the cleared altitude before the glideslope and go into ALT*. While it is doing this, it will ignore the glideslope completely and you will fly level, past the glideslope intercept point, leaving you above the glide!

I think you've just confused the issue a bit there Uplinker! :O If you're below the glide ("lozenge coming down towards the altitude lubber line") and the aircraft enters ALT* whilst you have GS armed.....it will capture the Glide - ALT* doesn't disarm GS (blue). The only caveat there is that the glide must have been armed for approx 2-3 seconds at least prior to GS* otherwise it will fly through (something to do with an integrity check). Your method of V/S -200'/min is spot on to prevent the ALT* but if it does occur its not an issue. Perhaps on the older 'Bus's it is?

The scenario where problems occur is when you're above the glide with a lower ALT set set and the risk of early ALT* prior to GS* - see my previous post.

A4

[fade to grey]

All this talk of gear.....presumably everyone has the speedbrake right out already ?

I'd also say I saw alot of folks realise they were high/fast, and tickle the speedbrake out, stick it back in......2 minutes later out again.....if it's going pear shaped get it out and keep it out until the situation is definitely sorted.

[Uplinker]

Hi A4,

I agree that I may have confused WhySoTough with a refinement that he is probably not ready for yet.

However, on the Airbusses I fly; ALT* does block G/S capture if the two points are co-incident in time and space. While ALT* is active and the aircraft is capturing the selected altitude, it will ignore the glide and not capture it - I've proved that several times, to my own embarrasment :rolleyes:! - then you have to intercept the glide from above, (or go manual).

Perhaps they fixed this glitch in later models?



U

[Microburst2002]

In order to avoid an unstabilized approach, you need every day to evaluate the variables of each approach. For instance:

weight
wind
traffic behind
G/S capture altitude

In a day with high weigh, tail wind, capture at 1,700 ft and a traffic behind pushing you... You better be proactive or it is likely you will be unstabilized if you "sleep" and just do what you do every day.

In a day with low weight, head wind, capture at 3,000, you are number one and number two is 10 minutes away... Relax, man.

Get used to take into account those variables, and others that I may have forgotten to mention, and act accordingly. In the 320, when some of those variables are against me, I configure without delay, flaps 1 so as to be with S no later than at the G/S, flaps 2 if at or below 2,000 ft capture. And I keep configuring non stop until fully configured. If there is maintain 160 til 4, managing by 4 with full should do. If there is strong tailwind and high weight and you feel the engines almost idle, it will take long to decelerate: manage speed at 6 or 5 miles instead.

In the relaxed day I try to make low drag low noise, I delay flaps, gear, etc... But don't relax too much. Aim to be stabilized at 1,500 ft, so you have a buffer.

[thermostat]

The Airbus doesn't need ATC to fly an approach. It can do that by it's self. ATC need to be a "king in his own castle".
Some things to follow.
1. never let ATC fly your airplane. If you don't agree with an instruction, don't accept it.
2. The 320 (if you are on the green approach line) will automatically activate the approach at 15 nm from touch down.
3. Situation awareness is paramount. You must know where you are at all times. Use you RMI.
4. A 3 degree slope is 318 feet down for every NM forward. That's the gradient.
5. If you have to capture the GS from above, the FCOM says; altitude alert above aircraft altitude, ILS (GS) armed, select 1500 fpm down. This way you won't run into the ALT* problem. Further to that, rate of descent and ground speed work together. The faster the GS, the greater the ROD has to be. On the 320 it's simple. Look at the GS on the ND (lets say it's 170 kts), add one to 17 = 1800 FPM, your correct ROD for a 6 degree slope. This allows 3 deg slope to capture a 3 deg slope.
So GS140 = 1500 fpm, 150 = 1600 fpm etc. Max is 2000 fpm. No guess work, and no hassle. Everything to do with flying and computers is mathematical.
Have fun.
T