RUNWAY EXCURSIONS -AN ATC PERSPECTIVE ON UNSTABLE APPROACHES
What is a Runway Excursion? A runway excursion as “An event in which an aircraft veers off or overruns the runway surface during either take-off or landing.” Runway excursions lead to more runway accidents than all the other causes combined.
What causes a Runway Excursion? There are many factors that may cause a runway excursion, including;-
Adverse weather conditions.
What is an Unstable Approach?
An unstable approach is simply an approach that does not meet the criteria for a stable approach established by the aircraft operator.
Criteria for Stable Approaches.
On the correct flight path.
ILS Approach – ILS within 1 dot of the localiser and glide slope.
Visual Approach – Wings level at 500 feet AGL.
Circling Approach – Wings level at 300 feet AGL.
Only small heading and pitch changes required.
Speed within +20/-0 kts of reference speed.
Aircraft must be in proper landing configuration.
Maximum sink rate of 1,000’ per minute.
Appropriate power settings applied.
Briefings and checklists complete.
During IMC – Stable by 1,000 feet AGL.
During VMC – Stable by 500 feet AGL.
If the approach is not stable by 1,000 feet AGL or 500 feet AGL (depending on weather conditions), or if the approach becomes unstable below these altitudes, the pilot should initiate a missed approach/go around.
The pilot may initiate a go around at any time above or below these altitudes if deemed necessary.
It is possible for a pilot to initiate a go around even after touchdown on the runway, but not after the thrust reversers have been deployed.
For ATC purposes, in the most basic terms, if an arriving aircraft is too high or too fast, the approach will most likely be an unstable one.
What Role does Air Traffic Control play?
ATC can influence the safety and stability of an approach in two general areas. First, the instructions and clearances that are issued to the pilot can be significant factors in determining if an approach will become unstable.
For example, if a descent clearance is delayed and the aircraft is close-in to the runway, the aircraft may be high on the approach, leading to a flight profile that is both above the glide slope and at a high sink rate.
Second, ATC plays a critical role in providing information to the pilot. For example, if the surface winds suddenly shift from a headwind to a tailwind, the aircraft’s flight profile may be significantly affected.
If the wind information is promptly and accurately relayed to the pilot by ATC, the pilot would then be able to anticipate and compensate for the effects of the wind, making the necessary corrections to ensure a stable approach or request an alternate runway.
ATC Best practices to Avoid Unstable Approaches.
A stable approach ends with the successful completion of the landing and rollout. The stable approach may begin, however, 100 miles or more from the airport. En-route control and terminal approach control both play key roles during the initial descent phase and in positioning the aircraft on the final approach.
The tower local control also has a very important role in determining the outcome of the approach and landing.
General ATC Best Practices.
Inform the pilot what to expect regarding runway assignment, type of approach and descent/speed restrictions so the proper planning and execution can be conducted.
Stable approaches require predictability and planning.
Avoid last minute changes unless absolutely necessary, and advise the pilot as early as possible when changes are anticipated.
Ensure the runway assignment is appropriate for the wind.
Excessive tailwinds or crosswinds can lead to unstable approaches, and especially when the runway is wet or contaminated, are often associated with runway excursions.
Issue accurate and timely information related to weather conditions, wind and airport/runway conditions.
When conditions are rapidly changing, promptly inform the pilot of all significant changes.
Keep the overlying control facility (approach control or en-route) advised of changing conditions as well.
Apply appropriate speed control/restrictions. Assigning unrealistic or improper speeds, both fast and slow, or assigning speed control close-in to the runway may lead to unstable approaches.
Be responsive to pilot requests, especially those involving speed assignments, descent requests or runway/approach assignments.
If you are unable to accommodate the pilot’s request, advise the pilot of the reason, and if able, offer an alternative.
Arrival and Approach Best Practices Avoid routine vectoring of aircraft off a published arrival procedure to shorten the flight path. Unexpected shortcuts may lead to insufficient time and distance remaining to maintain the desired descent profile, and causing the aircraft to be high on the approach.
Avoid close-in turns to final. Give preference to approaches with vertical guidance over approaches with only lateral guidance. Approaches with vertical guidance (ILS, GBAS, LPV, and Baro-VNAV) assist the pilot in maintaining the proper descent profile, resulting in stable approaches.
When smaller aircraft are sequenced behind larger aircraft the pilot of the smaller aircraft may elect to stay above the glide slope in order to maintain wake turbulence separation from the larger aircraft.
Controllers should be aware that this combined with an ATC higher speed instruction may lead to an unstable approach.
Avoid instructions that simultaneously combine a descent clearance and a speed reduction. Many aircraft are not capable of performing a simultaneous descent and speed reduction while maintaining a stable approach profile. Specify which action you expect to be performed first.
Issue appropriate and accurate track mile information from the airport or approach fix in a timely manner, as required. Comply with requirements related to capturing the glide slope from below. Vectoring for an approach that places an aircraft on the final approach course above the glide slope is a leading cause of unstable approaches
Tower Best Practices.
Avoid close-in, last second runway changes, even to a parallel runway. To comply with the company’s operational procedures and requirements, the flight crew must have time to properly brief the approach and missed approach procedure to the runway being utilised. Even though a pilot may accept a runway change, the result may be an unstable approach.
Avoid pattern entry instructions that require the pilot to turn final close-in to the airport, especially with turbojet aircraft. For example, instructing an aircraft to enter on a close-in base leg may result in an unstable approach.
Issue timely weather information. When the surfaces winds are rapidly changing, ensure the pilot has the most current information. Solicit pilot reports on weather conditions and runway braking action and disseminate the information in a timely manner.
Be alert for signs of an unstable approach. For example, if an aircraft is above the glide slope altitude at the final approach fix, then an unstable approach is likely.
When a possible unstable approach is detected, query the pilot and then be responsive to the pilot’s requests.
Many factors can lead to an unstable approach, which in turn, may lead to a runway excursion. While a large number of these are beyond the control of ATC, controller involvement can play an important role in contributing to safe, stable approaches and reducing the risk of runway excursions.
Recognising and identifying unstable approaches, issuing proper clearances and providing timely and accurate weather information are important actions that ATC can perform to significantly reduce the risk of runway excursions.
Pilots are under pressure to achieve a stabilised approach for a number of reasons:
Safety: unstable approaches have either directly or indirectly been the cause of several incidents and accidents including Runway Excursions.
Economic: a missed approach can eliminate all profit from a flight. Due to fuel constraints it may also result in a diversion to an alternate aerodrome.
Ultimately it remains the responsibility of the Pilot in Command to decide not to continue an approach if, in their opinion, the approach is becoming unstable. This decision can be made at any point during the approach and not just at the Stabilised Approach decision point. Nevertheless, in the chain of events that led up to an unstable approach.
Descent Planning and ATC Routing. When operating piston and light turboprop aircraft descent planning is somewhat straightforward as these aircraft operate at lower speeds and altitudes, and use propellers which add drag.
Jet aircraft (and larger turbo prop aircraft) have a very ‘clean’ design which offers minimal drag in order to achieve high cruising speeds. Therefore jet aircraft often have a tendency to be ‘slippery’, i.e. they require a lot of distance to descend and/or slow down. Further, jet aircraft operate at higher altitudes making the descent longer, which can compound any errors.
The whole situation is exacerbated by the use of modern high-bypass turbofan engines, which produce a significantly higher residual thrust at flight-idle than older, low-bypass or pure turbojet, engines fitted to the previous generation of jet aircraft.
Large aircraft are often fitted with a Flight Management System (FMS) which performs the descent calculations. Based on the planned route the FMS continuously calculates and updates a vertical profile and a speed profile, collectively referred to as a descent profile in this assessment.
The vertical profile relates to the aircraft’s planned level at any given point during the descent, and the speed profile relates to the target speeds for each segment of the descent.
The speed profile is calculated by a number of factors such as speed limits, wind and Cost Index.
With the necessary involvement of ATC instructions, the FMS calculated descent profile is not often flown. It is therefore important that the flight crew keep a mental model (situational awareness) of the profile as the constantly changing environment can quickly alter the remaining track mileage
Descent planning for jet aircraft is often based on a ‘three times’ rule of thumb, or a variant thereof. As an example, with 100 nautical track miles remaining the aircraft should be at approximately 30,000 ft on its descent profile. Extra distance is then added for deceleration. With larger aircraft such as the B747 or A380, momentum plays a bigger role hence a longer distance for deceleration is required.
Other factors may also play a role during manual descent planning, such as speed instructions from ATC, wind, and turbulence.
Ideally descents usually take place with little or no thrust, hence immediate measures that are available to ‘catch’ the profile are speed brakes and increased speed.
Speed limits tend to apply at lower levels (e.g. 250 knots below FL100) and speed brakes often become less effective as the aircraft decelerates. Hence towards the latter stages of the descent, drag may be increased by early deployment of gear and flaps.
However this is not a preferred option as it increases system wear and may be inconsistent with local noise abatement procedures. Additionally, flap and gear deployment are almost always associated with airframe speed restrictions and increases in fuel burn.
Although the FMS will automatically try to adjust the descent profile for alterations, a point can be reached where the aircraft simply does not have sufficient distance to descend and decelerate.
Failure of the flight crew to anticipate ATC instructions and consequently alter the descent profile can result in the aircraft being too high to make the approach. Should this occur early in the approach the crew may request additional track miles. Should it occur late in the approach the crew may well decide to execute a missed approach?
One of the most critical elements is to ensure that the crew receive regular and accurate updates of the distance from touchdown (DFT) and is informed at the earliest opportunity of a change in routing; vectoring will significantly alter the track miles. This is especially important for planning purposes if the track miles are being reduced.
Approaches. Change of Runway.
Prior to arrival a number of tasks must be accomplished on the flight-deck. As an example the flight-deck must be configured for the approach, which would include setting all frequencies, minima, levels, speeds, routings etc. Following this a briefing is required.
Briefings are a component of Crew Resource Management (CRM) to assure ‘transparency’ i.e. that all crew are working to the same plan for both normal and abnormal events and will always include details of the Missed Approach Procedures (MAP) for the planned arrival runway.
The crew will also fly the approach expecting to “go-around” until the decision point (such as the Decision Altitude) at which time they decide to land.
Prior to the approach, the setup and briefing tend to be conducted reasonably early, usually well before top of descend.
A late runway change may not only imply a different routing for the aircraft, but also that the flight deck must be set up for a different approach on a different runway.
This will require a new briefing and the Flight Management Computer (FMC) to be reprogrammed. Therefore late runway changes tend to increase the flight deck workload significantly during an already busy flight phase.
This also applies to any changes to the standard MAP which, if not as published, should be communicated to the flight crew as early as possible. It is reasonable to assume that errors are more likely to occur as the workload increases.
Runway changes that result in more track miles remaining are generally easier to cope with as they provide additional time for the setup and briefing. With more track miles suddenly remaining the aircraft will be low on the ‘new’ profile which can be compensated for by reducing the rate of descend.
Further, a late change to a parallel runway with the same type of approach tends to be easier to cope with as the descent profile remains virtually the same and parallel runways often have the same MAP.
The most difficult runway change involves a change to a runway that results in less track miles remaining. As an example, a late change from 09 to 27 for an aircraft coming in from the east will probably result in a rushed setup and an abbreviated briefing and will, assuming the aircraft was on profile in the first place, suddenly put the aircraft high on the ‘new’ profile. In these instances additional track miles will probably be required.
Change of Approach – Precision/Non-precision.
There are fundamental differences in how different types of approaches are flown. The ILS is the most common approach used at large airports. An ILS approach is usually flown at 3º and allows most aircraft to fly a large part of the approach on autopilot. It also requires relatively little manipulation of the autopilot during the approach; it is mainly speed reductions that take place to allow flaps and gear to be deployed.
During an ILS approach the aircraft will continue to slow down and configure after becoming established on both the localiser and the glideslope. This means that the aircraft can maintain a relatively high speed until late in the approach, such as 160knots until four miles. However, it is very difficult for a modern aircraft (A330, B-737-800, etc.) to descend on the glide slope and slow down simultaneously; therefore the controller must allow for deceleration to final approach speed when the aircraft is approaching the glide slope interception point.
Flight crew requests for a slower airspeed during the final portion of the approach should be approved to the maximum extent possible.
Non-precision approaches result in a much higher workload as in many cases, the crew must manually control rate of descent or altitude. Although it can be flown on autopilot, more manipulation of the autopilot is required as the crew must continuously adjust the rate of descent.
The autopilot is usually disconnected earlier compared to a precision approach as the decision point (Decision Altitude) is higher.
Non-precision approaches may be offset from the runway which requires an element of manual handling late in the approach, and as they are not usually flown and practiced as frequently as precision approaches, it can result in the crew being less proficient.
Controllers should be aware that due to the increased workload and constraints for the aircrew in flying a non precision approach, when vectoring onto finals and should aim to position the aircraft on finals at a distance greater than normal, to assist the crew. However, an awareness of flight crew workload can assist in reducing cockpit workload. Based on these challenges, non-precision approaches tend to be carefully briefed.
A fundamental difference compared to a precision approach is speed management. As the speed changes during a non precision approach, the pilot needs to recalculate and manually adjust the rate of descent in order to remain on the correct glide-path.
Typically, as the aircraft is slowed, the initial calculated rate of descent will need to be reduced otherwise the aircraft will descend below the glide-path.
These changes significantly increase the cockpit workload and have been direct causal factors in many CFIT events.
However, if the speed is stable, then the rate of descent can be stabilised, reducing cockpit workload and allowing greater monitoring of the required track, aircraft configuration, check list procedures etc.
Non-precision approaches can also be steeper than precision approaches; hence the aircraft must be slowed down and configured earlier. Therefore it would be unreasonable to provide the pilots with any form of speed instructions after the Final Approach Fix (FAF).
In fact, many airlines train their crews to fly a non-precision approach at the final approach speed and therefore most crews would elect to slow down much earlier than when on an ILS.
Considering the above, a late change from a precision approach to a non-precision approach can be significant from a pilot’s point of view and may not always be feasible unless additional track miles are granted. This situation could occur should the glide-slope element of an ILS fail, reducing the approach to an LOC/DME approach.
A visual approach is usually flown manually and is mainly based on pilot judgment. Visual approaches mostly follow a standard traffic pattern, or variations thereof. Pilots sometimes request visual approaches at smaller airfields even if an instrument approach is available as they can be made shorter and thereby quicker.
A visual approach requires no instrument guidance, however flight crew will often use onboard navigation systems (if available) for reference.
Visual approaches can be associated with more pilot errors (including performing unstable approaches) than instrument approaches as they are more judgement based and less guidance is available.
Offering an aircraft a visual approach with short notice to expedite traffic flows will again result in a higher workload on the flight deck as a new briefing and strategy will be required.
Airline flight crews may be less proficient with visual approaches as they tend to be performed less frequently so, contrary to belief, offering a visual approach isn’t necessarily the aircrew’s preferred option.
Vectoring for Approach. Both lateral and vertical guidance must be provided for any type of approach. The lateral guidance can be determined by obtaining distance and bearing from a radio beacon of some sort (NDB, ILS, VOR, DME, LOC etc.), or by GPS.
During a precision approach the vertical guidance is based on the glide slope signal which is emitted from the side of the runway. Non-precision approaches do not provide a glide-slope signal (by definition) hence the vertical guidance is based on height/distance calculations using the DME, timing from a fix or by the FMS during a VNAV approach.
In this case it is often the Pilot Monitoring (PM) that provides the vertical guidance to the Pilot Flying (PF) by calling out the appropriate levels for each point in the approach.
This represents a significant increase in the flight-deck workload, and controllers should be aware of this and vector the aircraft onto finals at a greater distance, than they would for a precision approach. An aircraft can either self-position for an approach or be vectored.
Unstable Approaches – ATC Considerations. The aircraft must be lined up with the runway and at an appropriate distance. If the aircraft is not in the correct position the final descent cannot be commenced as the aircraft may be outside of the protected area, hence terrain separation cannot be assured. A descent at this point would be dangerous, particularly if in Instrument Meteorological Conditions.
Vectoring by ATC plays an important role in positioning an aircraft for an approach. The following two examples show a reference scenario during which an aircraft is correctly vectored for a precision approach and a scenario where unrealistic vectoring results in the aircraft either performing a missed approach and/or becoming unstable.
Descend Planning Requirements.
For the crew to be able to adequately perform descent planning, at least one of the following is required:
Adherence to the Flight Plan Route and Approach Procedure.
Local Knowledge of Potential Deviations.
Track Distance Information from the Approach Controller. To expect aircraft to always adhere to the planned route and approach procedure is impractical for ATC. Also, all pilots will not have experience with local ATC procedures. Therefore the option that provides most flexibility is provision of track distance information from the approach controller anytime the aircraft is deviated from the planned route and approach procedure.
Adherence to the Flight Plan Route and Approach Procedure. Based on the flight plan route,a descent profile can be calculated by the FMS. If the aircraft adheres to the planned route it should also adhere reasonably to the descent profile. Anytime ATC modifies the route some form of compensation will be required, such as a speed change or even speed brake deployment.
Unstable Approaches – ATC Considerations.
For ATC to keep all aircraft on their planned routes and descent profiles may not be practical in most traffic situations. Adjustments to speed, headings and levels are usually required to control traffic flow at busy times. Despite the aforementioned concerns regarding shortcuts and track mileage, some flight crew may deem that the shortcut is achievable and accept the shorter route to save time and fuel and to keep their place in the flow of traffic.
If ATC has to keep an aircraft above profile for operational reasons, it may be appropriate to adjust the aircraft speed e.g., assign a reduced speed) prior to commencement of descent in order to compensate for the “high” profile.
Most FMS programs keep the aircraft at the maximum altitude for as long as possible, using a profile with thrust at or near idle. As a consequence, there is little or no additional descent capability for the aircraft when descent is delayed significantly beyond the computed “top of descent point”, unless the flight crew uses increased descent speed, a longer flight path, or speed brakes.
Controllers should also be aware of the effect that encountering icing has on the operation of the aircraft during the descent. Most modern aircraft require a power setting above “flight idle” whilst descending in known icing conditions.
While planning the sequence of arrival or vectoring aircraft, controllers should be aware of this additional constraint and should be very careful not to position aircraft above the descent profile as the “recovery” to regain the profile will be much more difficult based on the additional thrust provided by the engines. If an aircraft is held high for any reason, it will probably end up high on the descent profile. Once the descent is granted it will again have to compensate by increasing its descent rate.
Local Knowledge. ‘Local Knowledge’ refers to the flight crew’s experience with a particular area allowing them to anticipate the ATC instructions associated with that area. As an example, certain airports publish arrival procedures that are seldom adhered to; instead an unofficial vectored route is provided which may be longer or shorter.
Pilots familiar with the approach will most likely position themselves high or low on the descent/approach in anticipation of the route change. Although the flight crew may be experienced, they may not be experienced with the arrival in question and will therefore be unable to anticipate ATC instructions.
Track Distance Information from Approach Controller In cases where aircraft are being vectored for an approach, provision of a regular and accurate distance to touchdown from the approach controller allows the flight crew to calculate their descent profile.
This is particularly important during Continuous Descent Approaches (CDA) as the margins for error are smaller. Obviously this information has to be provided reasonably early during the approach to enable adjustments to be made. Should the remaining track miles be provided/updated late in the profile it will be more difficult for the flight crew to make any necessary compensations?
Should the flight crew determine that the track miles proposed by the controller are inadequate, they may request additional track miles to enable them to comply with their criteria restrictions for maintaining a stabilised approach.
If the extra miles aren’t available and the crew continue with the approach then there is an increased risk that the approach may become unstable.
The ATC belief that in reducing the remaining track distance, it will help the flight crew, is not always true; it can significantly increase the flight-deck workload as the crew must attempt to catch the “new” descent profile whilst trying to maintain a stabilised approach, which increases the associated risks.
Descent at Higher Speeds.
An aircraft descending at higher speeds (as an example, above 250 knots) will descend quicker if it accelerates as the Total Drag is higher. Going faster therefore increases the descend rate, which can be used as a means of keeping the aircraft on the vertical profile.
If no speed instruction is given to an aircraft it will probably descend at the optimum speed for the prevailing conditions as calculated by the FMS, and will probably descend at idle power.
Should ATC instruct an aircraft to decelerate to a lower speed, the rate of descent will decrease and the aircraft will drift above the descent profile?
At this point the only option is to use spoilers and/or to request more track miles.
An instruction to maintain a higher than normal speed is usually not a problem as the aircraft can simply add power to keep the aircraft on the descent profile.
An aircraft that is simultaneously descending and decelerating is dissipating both its kinetic and gravitational energy, which obviously would require a longer distance compared to an aircraft only decelerating, or only descending. As the aircraft decelerates less drag is available to dissipate energy which increases the distance further.
Descent at Lower Speeds.
On the contrary, an aircraft descending at lower speeds will descent quicker if it decelerates as Total Drag increases. This is the likely scenario during final approach when the aircraft is configured for landing.
Speed Instructions on Approach.
Higher speeds can, on the other hand, create problems as the aircraft gets closer to the airfield as it requires a certain distance to decelerate and configure for landing.
The events that lead to an unstable approach can already begin to transpire during the initial descent i.e. long before glide slope intercept.
Unstablised approaches increase risk in approach and landing. Excessive sink rates on approach while attempting to capture a glide path can result in a hard landing or even Controlled Flight into Terrain (CFIT).
An unstablised approach can also result in landing long or at an excessive speed which can result in an overrun.
Anytime the route is modified or speed instructions are provided the aircraft may need to compensate for the change by adjusting power, drag etc.
Larger route modifications obviously require larger aircraft adjustments. Similarly, if an aircraft is held high it will end up above its descent profile and will again have to compensate.
If significant shortcuts are provided during the descent a point can be reached where the aircraft requires additional track miles. Rather than help the flight crew, reducing the remaining track distance can significantly increase the flight-deck workload as the crew must attempt to catch the “new” descent profile while trying to maintain a stabilised approach.
An aircraft requires a significantly longer distance to simultaneously descend and decelerate compared to just descending or decelerating.
When providing aircraft with vectors for approach, early, regular and accurate track distance information from the approach controller increases the crew’s ability to calculate an accurate achievable descent profile and reduce the chances of an unstable approach occurring.
A late runway change significantly increases crew workload and increases the potential for error, which could result in an unstable approach. If the change results in a shorter route compared to the original route more track miles could be required.
Flight crew usually find non-precision approaches more complex as they include more elements and are not performed as often as precision approaches. Speed instructions to aircraft that are inside the FAF are not recommended. Due to the associated increase in cockpit workload the aircraft should be vectored for longer finals, for a non-precision approach, than for a precision approach.
Visual approaches and circling approaches are more error prone than full instrument approaches; if ATC do not offer these types of approaches the pilots will probably execute the approach that they have briefed and are prepared for, thus reducing the risk of an unstable approach occurring.
Instructing an aircraft to reduce speed during the upper parts of the descent will usually cause it to drift above its descent profile.
Instructing an aircraft to maintain a higher than normal speed during the upper parts of the descent will generally not result in problems with regards to maintaining the descent profile as power can be added.
Requesting that an aircraft maintain a certain speed during final approach may conflict with the requirements for a stable approach.
Controllers should be aware that the FMS and ILS equipment is designed so that the localiser is captured first then the glide-slope. If the glide-slope is captured before the localiser the aircraft may not be able to continue the approach without it becoming unstable and the associated risk of CFIT increases.
It is better for pilots and ATC to acknowledge that the approach is unstable and throw the approach away early, rather than fight it on the way down anticipating that they will have the approach stabilised by the minima e.g. 1000/500ft, only to go around at the stabilised approach point, or worse, continue to land.
Controllers should be wary of offering what they might consider to be as favorable alternatives e.g. cutting the a/c in early, offering the option of a visual approach etc. This may lead the flight crew into accepting an option that puts them into a situation where there is a significantly increased risk of the flight/ approach becoming unstable.
Potential Causal Factors of Unstable Approaches.
The following list suggests general causal factors of unstable approaches. Many of these are unrelated to ATC.
Weather e.g. turbulence, head/tail winds, avoidance, un-forecast.
Aircraft technical issues.
Late or incorrect crew briefings.
Pilot-mismanagement of aircraft energy (e.g. speed, altitude, power).
Other traffic (held high to avoid, sequencing to airport, high traffic density) .
Unclear communication: ATC-ATC, ATC-Pilot, Pilot-ATC.
ATIS: frequency of ATIS update, equipment to access ATIS (voice, ACARS), length of ATIS message (a requirement for short ATIS with only weather and runway has been expressed), lack of standardisation of format, lack of ATIS or shared ATIS frequencies causing garbling.
Overloading of human (controller/pilot) due to workload.
RT loading/congestion-held high beyond planned TOD.
Airspace constraints-not fit for purpose e.g. airspace size, complexity of procedures.
Early speed control-go down/slow down-unrealistic energy management expectations.
Vectoring-including intercepting G/S from above, tight intercepts for the ILS.
ATC change in routings-short cuts/changes to distance from TD.
Speed control restrictions versus aircraft configuration requirements.
Outside CAS-no speed/variable intentions/interpretations.
Late notice of runway change/type of approach.
Little/inaccurate Distance From Touchdown (DFT) information