UTM and Remote ID

Why this matters

When many drones from many operators fly beyond visual line of sight in the same area, nobody sees the whole picture, and traditional air traffic control was never designed to talk to hundreds of drones. UTM (UAS traffic management) is a system in which several service providers exchange flight plans automatically. ICAO’s framework, Edition 4 (2023), sets out its common principles. People on the ground also need to know whose drone is passing overhead, which is the job of Remote ID.

UTM architecture

• Operators submit flight plans through the USS (UAS service supplier) they use.
• A USS shares an operational intent, a set of volumes in space, altitude and time.
• The discovery and synchronization service (DSS) tells each USS which other USSs have plans in the same area.
• The authority publishes constraints, such as temporary no-fly zones.
• ASTM F3548-21 specifies USS interoperability, including strategic conflict detection before flight and monitoring whether flights conform to their plans.

The European Union uses the name U-space, under Regulation (EU) 2021/664, applicable from 26 January 2023. It requires four services in every U-space airspace: network identification, geo-awareness, UAS flight authorisation and traffic information. Weather information and conformance monitoring are optional services that Member States may require.

Status in Thailand: Aeronautical Radio of Thailand (AEROTHAI) is trialling AEROTHAI UTM at Wangchan Valley in Rayong, with a first demonstration on 1 September 2022. We found no CAAT or NBTC announcement that mandates UTM or Remote ID in general. Operators in Thailand must check CAAT’s latest announcements before real operations.

Checking conflicts between flight plans

Each flight plan is split into segments, each a box in space, altitude and time (plus a buffer). Two boxes conflict only when they overlap in every dimension; if they are separated in even one, there is no conflict.

import math

def intent(start, end, alt, speed, depart, seg=1000, half_w=100, buf=30):
    (x0, y0), (x1, y1) = start, end
    length = math.dist(start, end)
    vols = []
    for i in range(math.ceil(length / seg)):
        a, b = i * seg / length, min((i + 1) * seg / length, 1)
        xa, ya = x0 + a * (x1 - x0), y0 + a * (y1 - y0)
        xb, yb = x0 + b * (x1 - x0), y0 + b * (y1 - y0)
        vols.append((min(xa, xb) - half_w, max(xa, xb) + half_w, min(ya, yb) - half_w, max(ya, yb) + half_w,
                     alt[0], alt[1], depart + a * length / speed - buf, depart + b * length / speed + buf))
    return vols

def overlap(p, q):
    return all(p[2 * k] < q[2 * k + 1] and q[2 * k] < p[2 * k + 1] for k in range(4))

A = intent((0, 0), (6000, 0), (30, 90), 15, depart=0)
for delay in range(0, 601, 30):
    B = intent((3000, -3000), (3000, 3000), (50, 90), 15, depart=delay)
    clashes = [(i + 1, j + 1) for i, p in enumerate(A) for j, q in enumerate(B) if overlap(p, q)]
    print(f"B departs +{delay:>3} s: {len(clashes)} conflicting segment pairs {clashes}")
    if not clashes:
        break

B departs +  0 s: 4 conflicting segment pairs [(3, 3), (3, 4), (4, 3), (4, 4)]
B departs + 30 s: 4 conflicting segment pairs [(3, 3), (3, 4), (4, 3), (4, 4)]
B departs + 60 s: 3 conflicting segment pairs [(3, 3), (4, 3), (4, 4)]
B departs + 90 s: 3 conflicting segment pairs [(3, 3), (4, 3), (4, 4)]
B departs +120 s: 3 conflicting segment pairs [(3, 3), (4, 3), (4, 4)]
B departs +150 s: 1 conflicting segment pairs [(4, 3)]
B departs +180 s: 1 conflicting segment pairs [(4, 3)]
B departs +210 s: 0 conflicting segment pairs []

Remote ID

ASTM F3411-22a defines Remote ID message formats for both broadcast and network Remote ID. Broadcast messages come in several types, such as Basic ID, Location/Vector, Authentication, Self-ID, System and Operator ID. The US rule FAA 14 CFR Part 89, fully enforced since 16 March 2024, sets minimum data, such as the aircraft identifier, the position and altitude of both aircraft and control station, velocity, a time mark and emergency status, and sets performance requirements such as:

• At least 1 message per second.
• Broadcast no later than 1.0 second after measurement.
• Position within 100 ft (30.48 m) at 95% probability.

3GPP also specifies UAS identification and tracking over mobile networks in TS 23.256, relevant to drones using LTE or 5G.

FT100 = 100 * 0.3048
meas = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.4, 13.4, 14.4, 15.4, 16.4, 17.4, 18.4, 19.4]
lat = [0.3] * 20
lat[7] = 1.2
errs = [4, 6, 5, 8, 7, 12, 9, 6, 5, 11, 14, 10, 8, 7, 34, 9, 6, 5, 7, 8]

sent = [m + l for m, l in zip(meas, lat)]
gaps = [b - a for a, b in zip(sent, sent[1:])]
print(f"broadcasts {len(sent)}, largest gap {max(gaps):.1f} s, gaps over 1 s: {sum(g > 1.0 for g in gaps)}")
print(f"latency over 1 s: {sum(x > 1.0 for x in lat)}")
within = sum(e <= FT100 for e in errs) / len(errs)
print(f"position within {FT100:.2f} m: {within:.0%} (needs at least 95%)")

broadcasts 20, largest gap 1.9 s, gaps over 1 s: 2
latency over 1 s: 1
position within 30.48 m: 95% (needs at least 95%)

Module lab

Common mistakes

Summary

• UTM lets several USSs exchange flight plans through a DSS and check conflicts before flight.
• A conflict exists only when volumes overlap in every dimension; delaying or separating altitude resolves it.
• Part 89 requires at least one message per second, no more than 1 second latency and position within 30.48 m at 95%.
• U-space has four mandatory services; Thailand is still at the UTM trial stage.

Check your understanding

1. Two boxes overlap in space and altitude but not in time. Is there a conflict?
2. A 1 km segment flown at 20 m/s with a 30 s buffer: what is the time window of the first segment for a departure at 0?
3. What are the four mandatory U-space services?
4. How many metres is 100 ft?
5. What is the status of UTM in Thailand, according to the information we could verify?