HK AIR TRAFFIC CONTROL BLOG

[psychohk]

I am based in HK and regularly fly in and out of HKIA.

With the increase in traffic operating in and out of HKIA recently, I have noticed that separation between us(a private jet) and larger jets is getting reduced.
We have encountered wake turbulence of varying degrees consistently when approaching runways 07L/R. On our last approach to 07L, ATC approach controller got us to with 5.6 NM behind a B777.

The answer to your question quickly is 5NM, so in the case you mentioned you were issued a precautionary warning only. So what is our practice or required? ATC is REQUIRED to provide WAKE TURBULENCE SEPARATION (WTS). For RWY 07 there are many reasons why it may deteriorate below the prescribed standard. Poor controller judgement, one or more crews not following directed speeds, strong tailwind on base and headwind on final. If this eventuates:

A following aircraft that is positioned with less than the required WTS can

1. be removed by ATC from the sequence and repositioned

or

2. The following crew SHALL be advised, "C/s.... you are 4.6nm behind a Heavy, caution wake turbulence". If deemed relevant, and there is still significant closure, the amount of closure is to be mentioned. ATC is passive in that we don't ask, but passively wait to see if the crew requests to carry out a missed approach, as is their right and seek re-positioning. To my knowledge this has not occurred here.

Whilst it is done rarely if ever here, if the following were to have the preceding in sight and accept visual separation and continue on a visual approach, then then all responsibility for wake turbulence can be handed to the crew. i.e. for an aircraft on a visual approach, the spacing with preceding traffic is the responsibility of the following aircraft.

Since everyone is using VNAV for descents, we are all following the same vertical profiles, and therefore the smaller aircraft like us, and many others, have an increase risk of more severe wake turbulence from the ever growing larger jets.

From extensive research undertaken to try to minimise WTS, aircraft following identical flight paths are unlikely to encounter wake. LIDAR radar typically depicts wake descending below the flight path of an aircraft for approximately 100' and then levelling off. So the wake is resting below glide path and gradually being moved downwind. Lateral movement has the wake propagate laterally at approximately 5 kts from either wing tip in still air. So if you descend in trail on the same ILS final, in headwind or crosswind conditions, a vortex encounter is improbable. If however, there were a quartering tailwind on final, the wake may advance towards the threshold and the possibility is quite real. At HKIA the greatest threat is on base leg where there is a possibility that if you are below the preceding, you will fly through the wake of that aircraft.

What are the minimum separations between small and large jets? Does ATC factor in this to their planning when smaller jets follow the larger ones?

Rather than small and large, we operate in accordance with international weight categories. Other than BA41 from GFS and the very occasionally BE20, HK operates Medium, Heavy and Super categories. So whilst some of the BAC traffic is at the bottom end of the Medium weight category, they are considered the same as a B737 or A320. The more likely position for encountering wake from a preceding is on base leg, or if you are positioned on final 07R and cross behind the traffic ahead for 07L. Wake on departure is a threat, but for business aircraft the climb profile is usually radically different than other traffic.

The standards are:


Medium following a Heavy - 2 minutes on departure - 5nm in trail when inbound or crossing traffic not 1000' above or below you.
Medium following a Super - 3 minutes - 7nm & 1000' applies
Heavy to heavy - not applicable - 4nm in trail & 1000' applies
Heavy following a Super - 2 minutes - 6nm in trail & 1000' applies

Medium crews remember 2 and 3 minutes (behind a Heavy & a Super) + 5 and 7nm in trail
Heavy crews remember 2 minutes (behind a Super) +4 and 6nm in trail.

Any intersection departure other than J10 or J2 add 1 minute to timed departure standards. Also, timing is done from take-off roll, not rotation or airborne.


ATC is regularly trying to find efficiency in traffic sequences to minimise delays. So traffic following an A380 may be positioned on the South runway as will BAC and Cargo arrivals. To make this effective, it permits the sequence to compress if traffic can be positioned to take advantage of it. IFR separation allows for traffic to be staggered North and South at 2.5NM. Under ideal conditions, TWR can accept visual separation between the two finals and permit simultaneous landings. Difficult to achieve on 07 because of the close base.

So as mentioned above, where the major threat is on base leg, if we run North/South landings, controller technique should be to have the preceding heavier aircraft as low as possible on base and then retain vertical separation (1000' above) until the following intercepts final and is clear of the flight path of the other aircraft. There is no WTS consideration between two aircraft on different runways at HKIA due to the physical displacement between them.

Also can we request increased separation from ATC and will they be willing to comply?

Consider how may airlines, different types and business aircraft that operate into HKIA. Other than international standards, what justification is there to arbitrarily increase spacing? The industry is crying out for predictability. If APP and TWR were to conduct a personalised Q&A with each aircraft they handle on what their preferences are, I think you'll understand how futile it would be. Especially when you are part of a sequence that spans more than one hour of continuous traffic, then as you are being positioned on base you request additional spacing behind the Heavy in front. How much? What are the consequences for other traffic? On departure if you are number one at the hold, you're given line up with an inbound landing on final and as you enter the runway you announce you require not 2 but 3 minutes separation with the preceding departure.
Would you consider asking in LHR, JFK or ATL? ATC operates to provide separation using international standards, not aircrew preference.

These same topics have been asked by many business crews. Thanks for submitting to allow a broader education on them.