Steep Glidepath Factors
Thread Starter
Join Date: Jul 2008
Location: UK
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
Steep Glidepath Factors
I'm carrying out an investigation into STOL operations and in particular the affect of a steep (>4 degree) Glide Path at an airport such as LCY versus a standard 3 degree GP at most other airports.
Whilst the start of descent wll clearly be much later, what other operational differences may there be? Will speeds vary greatly? tolerances on the GP/Localiser?
In particular i'm interested to know of any differences in factors afftecting decsion making should a problem occur. Given the steep approach, are there less options in the event of a situation at the top of descent as opposed to a standard 3 degree approach?
Thanks in advance!
Whilst the start of descent wll clearly be much later, what other operational differences may there be? Will speeds vary greatly? tolerances on the GP/Localiser?
In particular i'm interested to know of any differences in factors afftecting decsion making should a problem occur. Given the steep approach, are there less options in the event of a situation at the top of descent as opposed to a standard 3 degree approach?
Thanks in advance!
rl82 Aircraft flying steep approaches usually require more drag to stabilise the flight path, thus full landing configuration (and airbrake) may used from the start of descent.
Normally the same airspeeds apply. Some aircraft may fly fast to compensate for reduced flare performance, but this might be self limiting on a short runway – normally associated with ‘STOL’.
There will be differences in the ILS sensitivity, a greater beam cross-section with increasing approach path angle, but most airports adjust the transmitter beam-width characteristics. There may be similar problems with PAPI and approach lights.
The descent rate is approx twice the normal rate, thus there is less time for flight path correction and decision making. However, the options are much the same: fly the aircraft, assess the situation, and follow procedures.
Those aircraft certificated for ‘STOL’ have to demonstrate a stable approach requiring drag (as above), a sufficient margin of control – normally 2 deg above the approach glidepath, which also implies good control responsiveness factor (getting back to the GS quickly).
The aircraft must have good flare characteristics – the ability to quickly access lift to arrest the descent, preferably from a low flare height. This characteristic also confirms the ability to conduct a normal go-around, a certification demonstration which also includes an engine failure at the critical point.
Systems changes may include autopilot approach gain sensitivity and EGPWS alerting boundaries; these are normally selected by the crew.
Normally the same airspeeds apply. Some aircraft may fly fast to compensate for reduced flare performance, but this might be self limiting on a short runway – normally associated with ‘STOL’.
There will be differences in the ILS sensitivity, a greater beam cross-section with increasing approach path angle, but most airports adjust the transmitter beam-width characteristics. There may be similar problems with PAPI and approach lights.
The descent rate is approx twice the normal rate, thus there is less time for flight path correction and decision making. However, the options are much the same: fly the aircraft, assess the situation, and follow procedures.
Those aircraft certificated for ‘STOL’ have to demonstrate a stable approach requiring drag (as above), a sufficient margin of control – normally 2 deg above the approach glidepath, which also implies good control responsiveness factor (getting back to the GS quickly).
The aircraft must have good flare characteristics – the ability to quickly access lift to arrest the descent, preferably from a low flare height. This characteristic also confirms the ability to conduct a normal go-around, a certification demonstration which also includes an engine failure at the critical point.
Systems changes may include autopilot approach gain sensitivity and EGPWS alerting boundaries; these are normally selected by the crew.
Moderator
It is worth keeping in mind that "STOL" is a peculiarly military thing involving reduced speed factors for takeoff and landing with significantly increased risks in the event of one going quieter than the other(s).
Civil aircraft which are represented as being STOL are not in that they observe normal certification standards (in the main) ... however, they have low stall speeds, excellent high lift systems at low speed, good roll control, etc. ... and have, as a result, shorter than "normal" takeoff and landing distances.
Civil aircraft which are represented as being STOL are not in that they observe normal certification standards (in the main) ... however, they have low stall speeds, excellent high lift systems at low speed, good roll control, etc. ... and have, as a result, shorter than "normal" takeoff and landing distances.
John, I beg to differ (slightly I think) – “STOL is a peculiarly military thing”.
IIRC ‘STOL’ was a special addendum to Canadian certification requirements (possibly FARs) and enabled DeH (Aaah) Canadian types to undertake unique operations, e.g. Dash 7 into Aspen and Vail.
The Canadian document (working paper 7… ??) was used as the basis for UK CAA certification of the BAe146 before the advent of JAR; which interestingly the 146/RJ did not meet due to the way in which the 2 deg margin was demonstrated vice tailwind and anti icing use.
My recollection of military STOL is associated with the Lysander, Shorts Pioneer(s), and then the Harrier; the first two types being more closely associated with ‘light’ civil ops. I exclude the rotary wing thingy’s.
rl82 Steep approaches also have a noise advantage; the BAe146 Flight Manual has a table relating approach noise and glideslope.
IIRC ‘STOL’ was a special addendum to Canadian certification requirements (possibly FARs) and enabled DeH (Aaah) Canadian types to undertake unique operations, e.g. Dash 7 into Aspen and Vail.
The Canadian document (working paper 7… ??) was used as the basis for UK CAA certification of the BAe146 before the advent of JAR; which interestingly the 146/RJ did not meet due to the way in which the 2 deg margin was demonstrated vice tailwind and anti icing use.
My recollection of military STOL is associated with the Lysander, Shorts Pioneer(s), and then the Harrier; the first two types being more closely associated with ‘light’ civil ops. I exclude the rotary wing thingy’s.
rl82 Steep approaches also have a noise advantage; the BAe146 Flight Manual has a table relating approach noise and glideslope.
Don`t forget spool-up times with fans/jets,unless you have a lot of drag;easier with t/prop a/c..
Join Date: Mar 2000
Location: Arizona USA
Posts: 8,571
Likes: 0
Received 0 Likes
on
0 Posts
Ah yes, spool-up times.
On the 'ole B707 straight-pipe powered airplanes (JT4A-powered) the spool-up time could be as long as 15 seconds...an eternity, when on short final.
With these airplanes, configure early, and keep the engines fully spooled up was the procedure, otherwise...well, it wasn't a pretty picture.
Crews adjusted, and all went well...after proper proper procedures were in place at knowlegeable carriers.
New folks...found out, soon enough.
On the 'ole B707 straight-pipe powered airplanes (JT4A-powered) the spool-up time could be as long as 15 seconds...an eternity, when on short final.
With these airplanes, configure early, and keep the engines fully spooled up was the procedure, otherwise...well, it wasn't a pretty picture.
Crews adjusted, and all went well...after proper proper procedures were in place at knowlegeable carriers.
New folks...found out, soon enough.
Registered User **
Join Date: Nov 2007
Location: -
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
I'm currently flying the Dash7 and to add my two cents, it all boils down to one's skill and judgement in the end. It may seem so, in certain operations like ours, where we do lots of bush and island hops into very short, next to nothing strips, with quite a steep descent angle, sometimes as steep as 7 degrees. bear in mind that the Dash 7 is fully certified for 7.5 degrees on the approach. From what I heard that is what Brymon used to do into London City, and I stand to be corrected on this.
Stablised by 500' is good if on a visual approach in accordance with ALAR's, otherwise by 1000' would be the normal case when in IMC. I find it better to stabilise a bit early when on a steep approach of more than 5 degrees since you have quite a bit of potential energy which is a good thing as it trades off for speed which inturn gives you more control to handle, and things don't seem to rush up on you. There again, I have seen more experienced hands simply fly it down to 300' and get stabilised by then on numerous occasions. The slower approach speeds on the Dash7 also contributes for this allowance in steep approaches for eg, at max landing weight of 42,000 lbs the Vapp at 45 flap is 86 knots, only. As long as your ROD doesn't exceed 1000' per min below 500' then I should say its normal. In response to what was asked as to whether the speeds vary greatly, well no, it shouldn't and if that is so, then its an approach going beans. If your skills are as sharp as a bushie, I would say you hardly would even touch the throttles and fish for the speed with attitude, your descent would be greater which is normal in STOL ops, the speeds should be steady and decaying smoothly. I would also reckon the glidepath would be more 'lively' since it's getting closer and you are higher than normal, so it is good practice to have the aircraft stablised early for this. Gears maybe delayed until a thousand, but get flaps in stages and condition levers to max at about 750' should do the trick nicely, with your 45 coming out by 500'. However, theory and explanations aside, when operating into bush and islands this changes and it is puerly on skill and judgement. You can have all the 'Gurus' preeching by the book stuff, but in reality it changes everyday. I stand to be corrected on all the above, so just mail away.
Stablised by 500' is good if on a visual approach in accordance with ALAR's, otherwise by 1000' would be the normal case when in IMC. I find it better to stabilise a bit early when on a steep approach of more than 5 degrees since you have quite a bit of potential energy which is a good thing as it trades off for speed which inturn gives you more control to handle, and things don't seem to rush up on you. There again, I have seen more experienced hands simply fly it down to 300' and get stabilised by then on numerous occasions. The slower approach speeds on the Dash7 also contributes for this allowance in steep approaches for eg, at max landing weight of 42,000 lbs the Vapp at 45 flap is 86 knots, only. As long as your ROD doesn't exceed 1000' per min below 500' then I should say its normal. In response to what was asked as to whether the speeds vary greatly, well no, it shouldn't and if that is so, then its an approach going beans. If your skills are as sharp as a bushie, I would say you hardly would even touch the throttles and fish for the speed with attitude, your descent would be greater which is normal in STOL ops, the speeds should be steady and decaying smoothly. I would also reckon the glidepath would be more 'lively' since it's getting closer and you are higher than normal, so it is good practice to have the aircraft stablised early for this. Gears maybe delayed until a thousand, but get flaps in stages and condition levers to max at about 750' should do the trick nicely, with your 45 coming out by 500'. However, theory and explanations aside, when operating into bush and islands this changes and it is puerly on skill and judgement. You can have all the 'Gurus' preeching by the book stuff, but in reality it changes everyday. I stand to be corrected on all the above, so just mail away.
Last edited by Dash7Ace; 8th Aug 2008 at 13:14.
PPRuNe Handmaiden
Lon City EGLC is 5.5 deg slope. Quite fun.
We have to record in the tech log if we do a landing at Lon City. I think it counts for "2" normal landings with respect to brakes and gear.
We have to record in the tech log if we do a landing at Lon City. I think it counts for "2" normal landings with respect to brakes and gear.
redsnail Re: “We have to record in the tech log if we do a landing at Lon City”
Interesting! Many years ago I observed an FAA trial at LCY which recorded landings for future design/certification specs of landing gear; the theory was that steep approaches would create higher touchdown loads. As I recall, the results showed no difference for the types assessed – 146 and Dash 7.
I assume that you are flying a ‘Hawker’ – another solidly designed ‘DH’ aircraft, which should not create any special problems. Excepting any unusual configuration on the approach – I suppose that you are not selecting airbrakes and flap together?
Is the tech log record a local or certification requirement?
Interesting! Many years ago I observed an FAA trial at LCY which recorded landings for future design/certification specs of landing gear; the theory was that steep approaches would create higher touchdown loads. As I recall, the results showed no difference for the types assessed – 146 and Dash 7.
I assume that you are flying a ‘Hawker’ – another solidly designed ‘DH’ aircraft, which should not create any special problems. Excepting any unusual configuration on the approach – I suppose that you are not selecting airbrakes and flap together?
Is the tech log record a local or certification requirement?
chevron, the original glide slope at LCY was 7.5 deg; this was used by Dash 7 aircraft landing on a short strip within the longer runway length. The reason for this angle appears to have been entirely due to noise considerations.
The 146 certification involved a compromise from the required 6 deg approach to provide adequate clearance of Canary Warf; 5.5 deg was allowed with the use of a high quality ILS glideslope beam and/or PAPI. Noise was also an issue, as was the obstacle clearance of the proposed bridge to the East.
To my knowledge, no two-stage approach was used or considered. Previous research work by RAE used initial approaches up to 6 deg with a change to 3 deg (4.5) below 1000ft; these options were not viable at LCY when landing to the East due to the close in obstacles.
IIRC some subsequent aircraft certifications have considered a ‘two-stage’ flare to overcome weaknesses in flare performance or to alleviate a higher than normal approach speed, but generally these have not been successful as the resulting landing distance increases rapidly (unable to claim 35 ft TCA).
The 146 certification involved a compromise from the required 6 deg approach to provide adequate clearance of Canary Warf; 5.5 deg was allowed with the use of a high quality ILS glideslope beam and/or PAPI. Noise was also an issue, as was the obstacle clearance of the proposed bridge to the East.
To my knowledge, no two-stage approach was used or considered. Previous research work by RAE used initial approaches up to 6 deg with a change to 3 deg (4.5) below 1000ft; these options were not viable at LCY when landing to the East due to the close in obstacles.
IIRC some subsequent aircraft certifications have considered a ‘two-stage’ flare to overcome weaknesses in flare performance or to alleviate a higher than normal approach speed, but generally these have not been successful as the resulting landing distance increases rapidly (unable to claim 35 ft TCA).
