Legalitys of one dot low during visual approaches?
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Legalitys of one dot low during visual approaches?
Ive heard that a few Operaters in this region quietley fly a one-dot low approach from 1000 ft AGL on displaced-threshold for landing runways served by ILS. Given good VMC by day, runway in sight, landing clearance obtained, and everything is ok, the theory is one can reposition the 50 ft crossing point to the (TO) runway threshold and not the DISPLACED (LDG) threshold (taking into account that the published OCA for a particular IFR minima is aplicable only in conditions of reduced visibility). This proc is supposed to assure wheel touchdown BY the 1000 ft markers and reduce the total landing roll, which from what I see it actualy does (say to make a desired pre-planned taxyway without wrecking the brakes and/or p!ssing the customers off).
Of course this isnt done at night or in IMC for obvious reasons.
Ive pulled it apart and cant see any impractical or safety-related reasons why one cant do it if one knows what hes doing especialy with regards to terrain etc as it relates to the published mandatory MaP or decision height. Im just asking here what would be the legal ramifications of doing such an approach, if any.
All replys welcome but Id be especialy interested in John Tullas comments.
Of course this isnt done at night or in IMC for obvious reasons.
Ive pulled it apart and cant see any impractical or safety-related reasons why one cant do it if one knows what hes doing especialy with regards to terrain etc as it relates to the published mandatory MaP or decision height. Im just asking here what would be the legal ramifications of doing such an approach, if any.
All replys welcome but Id be especialy interested in John Tullas comments.
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I'd also be interested in John_T's comments on this one, but the only thought occurring to me is that the legal ramifications will only become apparent if you havta face the judge. And the only reason that'd happen is if this practice resulted in a prang, for some reason. In that event, I suspect that you wouldn't have a legal leg to stand on - i.e. it WOULD most likely be determined as pilot error.
Having said that, I do pretty much the same thing all the time in the Kingair. Nothing has ever gone seriously wrong for me ... so far!
Having said that, I do pretty much the same thing all the time in the Kingair. Nothing has ever gone seriously wrong for me ... so far!
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Hopefully the experts will buy into this one viz., OzExpat (procedure design) and Overrun (airports engineering). While OzEx has put a pragmatic viewpoint above, perhaps some detail on the protected areas etc in the final section of the approach as modified might be illuminating ....... and, if the not so good vis case is considered, perhaps worrying ?
(a) The usual story with a displaced threshold is that there is an infringing obstacle on the approach which causes the displacement to be necessary. Airport runway design standards require that the obstacle clear approach angle be not greater than whatever depending on the classification of the runway. The numbers aren't so important for the pilot as much as knowing that there is an obstacle protection built into the runway landing threshold position which is appropriate to the aircraft and operation.
(b) With an ILS, the fan section GP makes the situation better than with, say, a T-Vasis (remember those, Slash ?) but, for a significant displacement, the aim of using the first section of the runway is not compatible with following the displaced ILS anyway ? .. and that gets us into discussions about unstable approaches which are not nice at the best of times ... especially if the conditions are not good.
What it really comes down to is how far do we push our luck ?
If the practice is subject to a rational assessment and management protocol ... ie
(a) airports engineering people provide a technical assessment of the obstacle problem
(b) some sort of sensible operational risk analysis is made
(c) the regulatory authority authorises the practice
(d) suitable training exercises, to the extent appropriate, are embodied in the operator's programs
then, fine.
However, one must be concerned about ad hoc, non-standard operational practices .... which is what I read into the story .... eventually it can get to the same sort of situation as unplanned airshow displays with an attendant unacceptably high level of risk.
Then again .... you could always bring me, OzEx and Overrun up to do a study on the problem ........
(a) The usual story with a displaced threshold is that there is an infringing obstacle on the approach which causes the displacement to be necessary. Airport runway design standards require that the obstacle clear approach angle be not greater than whatever depending on the classification of the runway. The numbers aren't so important for the pilot as much as knowing that there is an obstacle protection built into the runway landing threshold position which is appropriate to the aircraft and operation.
(b) With an ILS, the fan section GP makes the situation better than with, say, a T-Vasis (remember those, Slash ?) but, for a significant displacement, the aim of using the first section of the runway is not compatible with following the displaced ILS anyway ? .. and that gets us into discussions about unstable approaches which are not nice at the best of times ... especially if the conditions are not good.
What it really comes down to is how far do we push our luck ?
If the practice is subject to a rational assessment and management protocol ... ie
(a) airports engineering people provide a technical assessment of the obstacle problem
(b) some sort of sensible operational risk analysis is made
(c) the regulatory authority authorises the practice
(d) suitable training exercises, to the extent appropriate, are embodied in the operator's programs
then, fine.
However, one must be concerned about ad hoc, non-standard operational practices .... which is what I read into the story .... eventually it can get to the same sort of situation as unplanned airshow displays with an attendant unacceptably high level of risk.
Then again .... you could always bring me, OzEx and Overrun up to do a study on the problem ........
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And then there is a place like Quito, Ecuador. If one were to stay on the ILS Rwy 35 glide path to touchdown, one would touch down 830m beyond the threshold of the 3120m pavement. Since airport elevation is at 9228 MSL, it would not be an option to keep a heavy wide body pegged "bull's eye" all the way to touchdown. In fact, at 9850' (652') DA, one would transition to the VASI which slopes 2.5 dots below the ILS glide path.
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Slasher-
Regarding the "legality" -
Here in the US it's NOT legal. FAR 91.129 (e)(2),(3) states that the large/turbine powered a/c must stay at or above the electronic or VASI glideslope between the OM and MM. It makes no difference if it's an instrument approach or a visual, and makes no difference if it's IMC or VMC. There is also no exclusion for this FAR if it's a displaced threshold.
"Normal bracketing maneuvers" are permitted "for the purpose of remaining on the glideslope."
Along with the real world obstacle concerns voiced here, flying low may violate the noise restrictions for Stage III.
Rules may well be different in other states.
Regarding the "legality" -
Here in the US it's NOT legal. FAR 91.129 (e)(2),(3) states that the large/turbine powered a/c must stay at or above the electronic or VASI glideslope between the OM and MM. It makes no difference if it's an instrument approach or a visual, and makes no difference if it's IMC or VMC. There is also no exclusion for this FAR if it's a displaced threshold.
"Normal bracketing maneuvers" are permitted "for the purpose of remaining on the glideslope."
Along with the real world obstacle concerns voiced here, flying low may violate the noise restrictions for Stage III.
Rules may well be different in other states.
From ICAO Doc 8168 Vol I Part III, para 3.5.5.3
The aircraft should adhere to the on-course, on-glide path/elevation angle position since more than half course sector deflection or more tha half course fly-up deflection combined with other allowable system tolerances could place the aircraft in the vicinity of the edge or bottom of the protected airspace where loss of protection from obstacles can occur.
Of course, if you cancel IFR and conduct a visual approach I guess that would be perfectly legal...
The aircraft should adhere to the on-course, on-glide path/elevation angle position since more than half course sector deflection or more tha half course fly-up deflection combined with other allowable system tolerances could place the aircraft in the vicinity of the edge or bottom of the protected airspace where loss of protection from obstacles can occur.
Of course, if you cancel IFR and conduct a visual approach I guess that would be perfectly legal...
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Ah, Quito!
I lived there for a while, and could make your hair curl with some true stories. I do remember that someone took bits off the airplane on the top of the small hill short of 35 (Illimani, if memory serves), doing a shallow approach.
Dick W
I lived there for a while, and could make your hair curl with some true stories. I do remember that someone took bits off the airplane on the top of the small hill short of 35 (Illimani, if memory serves), doing a shallow approach.
Dick W
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At a recent FSF seminar in Oz, it was stated that 70% of CFIT accidents occured in the approach phase inside the OM which represents only 4% of flight time.
Be careful out there!
G'day
Be careful out there!
G'day
Quid
There is wiggle room within 91.129. Remember a VASI is just that, its not part of an ILS system, thus no OM or MM associated. As such on runways that don't have an associated ILS there is no way stay on till the MM. The reg states that the aircraft should remain an altitude at or above the glideslope until a lower altitude is necessary for a safe landing. Going into a place like John Wayne airport(5700ft), many find it necessary to go below to plant it in the TDZ. Its hairy in a NG let alone a 757 on a rainy day Many conversations with inspectors and our companies POI have led to an emphasis on the part of the reg that reads till a lower altitude is necessary for a safe landing
There is wiggle room within 91.129. Remember a VASI is just that, its not part of an ILS system, thus no OM or MM associated. As such on runways that don't have an associated ILS there is no way stay on till the MM. The reg states that the aircraft should remain an altitude at or above the glideslope until a lower altitude is necessary for a safe landing. Going into a place like John Wayne airport(5700ft), many find it necessary to go below to plant it in the TDZ. Its hairy in a NG let alone a 757 on a rainy day Many conversations with inspectors and our companies POI have led to an emphasis on the part of the reg that reads till a lower altitude is necessary for a safe landing
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You've caught me on the hop here J_T! It's been a real long time since I've had to consider action in the event of a displaced threshold, as regards ILS and VASIS/PAPI. I'll have to study it up and get back to you, unless someone else comes up with the answer, but I'm pretty sure the action differs somewhat, depending on whether it's a short-term temporary displacement, a long-term temporary displacement or permanent displacement.
The first thought that occurs to me, in the latter case, is that the VASIS/PAPI must be resited. This destroys harmonisation with the ILS GP and, if it's impractical to resite the GP (and then get the new arrangement properly flight checked), I suspect that the GP has to be turned off and appropriate Notams issued with relevant document amendments to withdraw the ILS procedure in favour of a LLZ or LLZ/DME approach.
This whole issue relates more to Operational Standards than to basic procedure design. Ops Standards is my area of specialisation, more so even than procedure design, but I haven't had to be too active in it due to the high priority that PNG CAA has been giving to procedure design over the years. So please don't take the above answer as gospel until I can check it out.
My first post was based on Slash's comment, quite rightly, that "Of course this isnt done at night or in IMC for obvious reasons". To conduct that sort of approach at night or in IMC would, most certainly, be courting trouble as there's usually no opportunity to see an obstacle and take timely avoiding action on the lower approach path.
Indeed, to have the GP radiating at all, when the THR is displaced could be a real operational worry. One must consider the lower wheel clearance over the THR and tail strike could become an issue for long body aircraft. Just thoughts off the top of me head at this stage.
The first thought that occurs to me, in the latter case, is that the VASIS/PAPI must be resited. This destroys harmonisation with the ILS GP and, if it's impractical to resite the GP (and then get the new arrangement properly flight checked), I suspect that the GP has to be turned off and appropriate Notams issued with relevant document amendments to withdraw the ILS procedure in favour of a LLZ or LLZ/DME approach.
This whole issue relates more to Operational Standards than to basic procedure design. Ops Standards is my area of specialisation, more so even than procedure design, but I haven't had to be too active in it due to the high priority that PNG CAA has been giving to procedure design over the years. So please don't take the above answer as gospel until I can check it out.
My first post was based on Slash's comment, quite rightly, that "Of course this isnt done at night or in IMC for obvious reasons". To conduct that sort of approach at night or in IMC would, most certainly, be courting trouble as there's usually no opportunity to see an obstacle and take timely avoiding action on the lower approach path.
Indeed, to have the GP radiating at all, when the THR is displaced could be a real operational worry. One must consider the lower wheel clearance over the THR and tail strike could become an issue for long body aircraft. Just thoughts off the top of me head at this stage.
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Male in the Maldives is a classic case.
They lenghtened the runway at the end before the GS, haven't moved the GS transmitter so you fly over 1000' or so to the "old" threshold and land etc. on 36
The approach lights are in the runway surface which can be used for rollout on 18, or for T/Off 36.
There are few hills in the Maldives, so the technical costs etc seem to be the problem to move the GS transmitter.
Be safe out there.
They lenghtened the runway at the end before the GS, haven't moved the GS transmitter so you fly over 1000' or so to the "old" threshold and land etc. on 36
The approach lights are in the runway surface which can be used for rollout on 18, or for T/Off 36.
There are few hills in the Maldives, so the technical costs etc seem to be the problem to move the GS transmitter.
Be safe out there.
Moderate, Modest & Mild.
Dunno about the "legalities" of it, Slash - I think most company procedures require a callout if you exceed 1 dot on G/S or LOC (and in some aircraft, 1 dot will activate a GPWS "GLIDESLOPE" at 1 1/3 dots below 1,000').......maybe that's why they restrict it to 1 dot low.
One dot at the OM is about 150' difference, and at the threshold would mean a gear height of about 30' instead of 50', so I don't see that they're really gaining too much.
The ones who worry ME, are the guys who intentionally fly FOUR REDS on a PAPI - "It's okay, I'm only JUST below the approach path."
Legally - dunno.
Company wise - I guess they're probably within the allowable tolerance if they stay just above 1 dot. The question is, if they are flying 1 dot, is the PNF calling "Glideslope" all the way down the hill?
Betcha if any of 'em prang though, the company will plead complete ignorance of the practice (I'll also bet that no official notice telling them to do it has been issued), and the pilots concerned will find themselves on the market.
IF it's what the company wants, tell them to put it IN WRITING, as a notice to ALL pilots!!
The name of the survival game is "cover your ass"!
One dot at the OM is about 150' difference, and at the threshold would mean a gear height of about 30' instead of 50', so I don't see that they're really gaining too much.
The ones who worry ME, are the guys who intentionally fly FOUR REDS on a PAPI - "It's okay, I'm only JUST below the approach path."
Legally - dunno.
Company wise - I guess they're probably within the allowable tolerance if they stay just above 1 dot. The question is, if they are flying 1 dot, is the PNF calling "Glideslope" all the way down the hill?
Betcha if any of 'em prang though, the company will plead complete ignorance of the practice (I'll also bet that no official notice telling them to do it has been issued), and the pilots concerned will find themselves on the market.
IF it's what the company wants, tell them to put it IN WRITING, as a notice to ALL pilots!!
The name of the survival game is "cover your ass"!
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Someone said a visual approach is just that, and ground avoidance is pilot's responsibility until over the black stuff. A lot would depend on the a/c type and wheel depth below eyeball. It would also depend on the dispalcement. RWY 33 at Madid where the displacement is 3500', it works well to fly the G/S to low level then adjust to touch at the threshold. The slide below the G/S takes place over the runway, so no obstacle can be interferring. It can also be done without de-stabilising the approach.
If the runway surface was suspected of not being excellent braking action, why leave 1000' or more behind you?? Same applies for tailwind.
For legality, is 1 dot low not within IR limits? If so then it should be safe and legal, or else the IR rules need adjusting.
There are airfields where there is no G/S guidance system. What then? or if it is u/s for arrival. Mark 1 eyeball and consumate skill! You'll NEVER get approval in writing.
If the runway surface was suspected of not being excellent braking action, why leave 1000' or more behind you?? Same applies for tailwind.
For legality, is 1 dot low not within IR limits? If so then it should be safe and legal, or else the IR rules need adjusting.
There are airfields where there is no G/S guidance system. What then? or if it is u/s for arrival. Mark 1 eyeball and consumate skill! You'll NEVER get approval in writing.
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I think the legal ICAO requirement is 1 dot high, zero low (sustained).
Thanks for your replys. Looks like the legaltys are spelt out black and white as far as the FAA is concerned but still a bit up in the air as far as ICAO goes. Its quite possible this one-dot low business may vary in the legal sense acording to the A.I.P. of each individual Contracting State.
Your dead right K.M.! You only need to acidentley bang the wingtip into a parked dunny truck, and the Inquisition cardinals and bishops will go right through everything including your prev rest period duration, what you had for breakfast, the CVR, FDR, checklist/briefing thoroughness etc etc etc, even if its entireley unrelated to the incident. If a one-dot low approach was discovered you can bet theyll search everywhere to see if they can hang that on you too!
RAT 5 as far as I know (and dont ask me who made THIS one up!) its only legal for RPT abv 5700 kg to continue, or commence, a non-guidance approach as long as the last guidance system fell over AFTER your arrival within 5nm of the ARP ( be it DME, or ILS G/S, LLZ marker-beacs, or VASIS). If it happens BEFORE you get there a D.C.A. dispensation is required to conduct a no-slope aproach. A good example is a pure NDB let-down for a straight-in, where the VASIS suddenley went bung during your inbound turn and your MORE than 5nm from the ARP. If another runway with a servicable vasis is available, then get to the cclg min and use it. If because of wx, wind, notams, terrain etc you cant, then to continue inbound and land off a no-slope aproach requires authorisation. In most cases ATC (the SATCO on duty or 'STAC' as hes known) has the power to act on behalf that countrys D.C.A. If the failure occurs WITHIN 5nm no authority is required and its up to the PIC to determine if he wants to continue and land (and considering also what the Company lays down, if any, regarding such an exercise).
I dont know any case anywhere where ATC has refused any aircraft a no-sloper. There attitude is if your ok then we are ok. And I dont even know if ATC units themselves are aware of the requirement (at least the ones around here!)
Remember Im talking strict legalitys here, not commonsense or practicality. Theres a gaping HUGE distinction.
Thanks for your replys. Looks like the legaltys are spelt out black and white as far as the FAA is concerned but still a bit up in the air as far as ICAO goes. Its quite possible this one-dot low business may vary in the legal sense acording to the A.I.P. of each individual Contracting State.
Your dead right K.M.! You only need to acidentley bang the wingtip into a parked dunny truck, and the Inquisition cardinals and bishops will go right through everything including your prev rest period duration, what you had for breakfast, the CVR, FDR, checklist/briefing thoroughness etc etc etc, even if its entireley unrelated to the incident. If a one-dot low approach was discovered you can bet theyll search everywhere to see if they can hang that on you too!
RAT 5 as far as I know (and dont ask me who made THIS one up!) its only legal for RPT abv 5700 kg to continue, or commence, a non-guidance approach as long as the last guidance system fell over AFTER your arrival within 5nm of the ARP ( be it DME, or ILS G/S, LLZ marker-beacs, or VASIS). If it happens BEFORE you get there a D.C.A. dispensation is required to conduct a no-slope aproach. A good example is a pure NDB let-down for a straight-in, where the VASIS suddenley went bung during your inbound turn and your MORE than 5nm from the ARP. If another runway with a servicable vasis is available, then get to the cclg min and use it. If because of wx, wind, notams, terrain etc you cant, then to continue inbound and land off a no-slope aproach requires authorisation. In most cases ATC (the SATCO on duty or 'STAC' as hes known) has the power to act on behalf that countrys D.C.A. If the failure occurs WITHIN 5nm no authority is required and its up to the PIC to determine if he wants to continue and land (and considering also what the Company lays down, if any, regarding such an exercise).
I dont know any case anywhere where ATC has refused any aircraft a no-sloper. There attitude is if your ok then we are ok. And I dont even know if ATC units themselves are aware of the requirement (at least the ones around here!)
Remember Im talking strict legalitys here, not commonsense or practicality. Theres a gaping HUGE distinction.
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In PNG, the usable range of a PAPI or T-VASIS is 4 NM. The requirement is for them to be used by turbojet aircraft. We have a wee confliction in our AIP at present where one section refers to "turbojet aircraft engaged in RPT operations" while, in another part, it simply refers to "turbojet aircraft". I understand that this is being worked on so that the requirement relates to the latter.
Anyway, if the system has failed and there's a Notam on it, there is an automatic 7 days dispensation. Up until very recent times, it was possible for an operator to obtain a further dispensation, for a prolonged system outage, but a recent executive decision stated that no such dispensations will be available. This will mean that turbojet operations to the affected runway will not be authorised.
I don't know if this decision has yet been notifed to the industry, so you might have heard it here first! I feel sure that there will be an objection or two and there could be an awful lot of brown stuff impacting fans in PNG, in the very near future.
If the system fails during the landing approach, it is the subject of an Air Safety Incident Report. The pilot will observe company SOP in deciding whether or not to continue and land but, whether the aircraft lands or not, the ASIR is required.
Anyway, if the system has failed and there's a Notam on it, there is an automatic 7 days dispensation. Up until very recent times, it was possible for an operator to obtain a further dispensation, for a prolonged system outage, but a recent executive decision stated that no such dispensations will be available. This will mean that turbojet operations to the affected runway will not be authorised.
I don't know if this decision has yet been notifed to the industry, so you might have heard it here first! I feel sure that there will be an objection or two and there could be an awful lot of brown stuff impacting fans in PNG, in the very near future.
If the system fails during the landing approach, it is the subject of an Air Safety Incident Report. The pilot will observe company SOP in deciding whether or not to continue and land but, whether the aircraft lands or not, the ASIR is required.
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Regarding the lack of PAPI/VASI:
In many European (Continental) states, it was common, until a few years ago, that if there was an ILS there were no PAPI/VASI's as back up. So, when the ILS was on maintenance-u/s etc. it was mark 1 eyeball and consumate skill, once again. There certainly was no effect on the use of the runway.
AMS was one of these airfields, but now it has PAPI backups. Whether this is no a JAA requiremnet I do not know. Germany was another country that had no backups; I'm not sure the situation there now. Thus I wonder if the preceeding comments about dispensations etc. are under FAA (or other) rules?
In UK it was reuqirement of base training and the type rating test to fly an approach without visual guidance. An excellent exercise that every pilot should be able to do. Given the number of airfields in European tourist destinations that are regularly used by many charter a/c of every type, and which have no ILS, only non-precision and PAPI's, it is essential to be able to fly an approach with mark 1 eyeball. Either the PAPI's could be u/s, often after violent TS's. or uncertified awaiting flight testing, or just on maintenance. To maintain the schedules the runways have to remain in use. It has been the case at some fields where the G/S was 3.25 and the PAPI's 3.00. Odd but confusingly true.
I was always taught that if there is a discrepancy between electronic and visual aid G/S, fly the electronic one. However that could be wrong due interferance and you should be able to ascertain that.
One things for sure with PAPI's, 4 of any colour is no guidance, especailly green; cos then you are very low!!!!
In many European (Continental) states, it was common, until a few years ago, that if there was an ILS there were no PAPI/VASI's as back up. So, when the ILS was on maintenance-u/s etc. it was mark 1 eyeball and consumate skill, once again. There certainly was no effect on the use of the runway.
AMS was one of these airfields, but now it has PAPI backups. Whether this is no a JAA requiremnet I do not know. Germany was another country that had no backups; I'm not sure the situation there now. Thus I wonder if the preceeding comments about dispensations etc. are under FAA (or other) rules?
In UK it was reuqirement of base training and the type rating test to fly an approach without visual guidance. An excellent exercise that every pilot should be able to do. Given the number of airfields in European tourist destinations that are regularly used by many charter a/c of every type, and which have no ILS, only non-precision and PAPI's, it is essential to be able to fly an approach with mark 1 eyeball. Either the PAPI's could be u/s, often after violent TS's. or uncertified awaiting flight testing, or just on maintenance. To maintain the schedules the runways have to remain in use. It has been the case at some fields where the G/S was 3.25 and the PAPI's 3.00. Odd but confusingly true.
I was always taught that if there is a discrepancy between electronic and visual aid G/S, fly the electronic one. However that could be wrong due interferance and you should be able to ascertain that.
One things for sure with PAPI's, 4 of any colour is no guidance, especailly green; cos then you are very low!!!!
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If an airport operator has displaced a threshold,for what ever reason,shouldn't it be subject to notam,and subseqently any associated approach guidance system be notam'ed as U/S?.
In saying that,any visual approach is made at pilot discretion,usually in accordance with any AFM or company OOps manual.
I would be rather reluctent,apart from using local knowledge and experience,to use any approach guidance system that is associated with a displaced threshold.
In my neck of the woods,when a displaced threshold is in operation,it is marked with lights and ground markings,and in some cases,a portable TVASI or PAPI,which will be notamed with the actual glidepath the system provides.Again,refer to AFM and OOps manual for compliance(and relevant landing charts for that matter),otherwise,its a visual approach!
In saying that,any visual approach is made at pilot discretion,usually in accordance with any AFM or company OOps manual.
I would be rather reluctent,apart from using local knowledge and experience,to use any approach guidance system that is associated with a displaced threshold.
In my neck of the woods,when a displaced threshold is in operation,it is marked with lights and ground markings,and in some cases,a portable TVASI or PAPI,which will be notamed with the actual glidepath the system provides.Again,refer to AFM and OOps manual for compliance(and relevant landing charts for that matter),otherwise,its a visual approach!
Moderator
Yowie,
Your thoughts are very relevant to a temporary displacement (typically due to MWP/WIP) .. the main discussion, though, is to do with permanent displacement (typically due to a permanent obstacle in the approach splay) with the landing aids sited to suit ongoing operations ...
Your thoughts are very relevant to a temporary displacement (typically due to MWP/WIP) .. the main discussion, though, is to do with permanent displacement (typically due to a permanent obstacle in the approach splay) with the landing aids sited to suit ongoing operations ...
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RAT5, I was at a presentation some years ago about runway utilisation. It appears that one solution to speeding up departure rates on an intersecting runway is to have a permanently displaced threshold on the landing runway (given that it is long enough not to impose landing distance penalties) - since landing, crossing traffic will transit the intersection at a much faster speed. Madrid RW33/RW36 was cited as an example. So landing short there will interfere with that process.